Littérature scientifique sur le sujet « Pyrroline-5-carboxylate »

Aroma is an important economic trait of vegetable soybeans, which greatly influences their market value. The 2-acetyl-1-pyrroline (2AP) is considered as an important substance affecting the aroma of plants. Although the 2AP synthesis pathway has been resolved, the differences of the 2AP synthesis in the aromatic and non-aromatic vegetable soybeans are unknown. In this study, a broad targeted metabolome analysis including measurement of metabolites levels and gene expression levels was performed to reveal pathways of aroma formation in the two developmental stages of vegetable soybean grains [35 (S5) and 40 (S6) days after anthesis] of the ‘Zhexian No. 8’ (ZX8, non-aromatic) and ZK1754 (aromatic). The results showed that the differentially accumulated metabolites (DAMs) of the two varieties can be classified into nine main categories including flavonoids, lipids, amino acids and derivatives, saccharides and alcohols, organic acids, nucleotides and derivatives, phenolic acids, alkaloids and vitamin, which mainly contributed to their phenotypic differences. Furthermore, in combination with the 2AP synthesis pathway, the differences of amino acids and derivatives were mainly involved in the 2AP synthesis. Furthermore, 2AP precursors’ analysis revealed that the accumulation of 2AP mainly occurred from 1-pyrroline-5-carboxylate (P5C), not 4-aminobutyraldehyde (GABald). The quantitative RT-PCR showed that the associated synthetic genes were 1-pyrroline-5-carboxylate dehydrogenase (P5CDH), ∆1-pyrroline-5-carboxylate synthetase (P5CS), proline dehydrogenase (PRODH) and pyrroline-5-carboxylate reductase (P5CR), which further verified the synthetic pathway of 2AP. Furthermore, the betaine aldehyde dehydrogenase 2 (GmBADH2) mutant was not only vital for the occurrence of 2AP, but also for the synthesis of 4-aminobutyric acid (GABA) in vegetable soybean. Therefore, the differences of 2AP accumulation in aromatic and non-aromatic vegetable soybeans have been revealed, and it also provides an important theoretical basis for aromatic vegetable soybean breeding.

Abstract Hypoxia is a common feature of glioblastoma, and a known driver of therapy resistance in brain tumours. Understanding the metabolic adaptations to hypoxia is key to develop new effective treatments for patients. A recent screening study highlighted Pyrroline-5-carboxylate reductase-like (PYCRL) as one of the top three genes that allowed tumour survival in hypoxia. PYCRL is one of the three enzymes involved in proline biosynthesis along with the mitochondrial pyrroline-5-carboxylate reductase 1 and 2 (PYCR1/2). The latter use glutamine as the carbon source to fuel the pyrroline-5-carboxylate (P5C)-to-proline reaction, whereas the cytosolic PYCRL is known to use ornithine to produce proline. Our investigations have shown that PYCRL differs from PYCR1 and 2 in the impact on cellular redox, which is a critical factor in hypoxic survival. Our data suggest that PYCRL activity is required for normal regulation of glioblastoma cell growth and the ability to deal with cellular stress, and that this enzyme may therefore represent a novel target in the treatment of these devastating tumours. Importantly, our study also begins to provide much-needed clarity over the network surrounding proline metabolism and redox maintenance.

The synthesis of citrulline from glutamine was quantified in enterocytes from pre-weaning (14-21 days old) and post-weaning (29-58 days old) pigs. The cells were incubated at 37 degrees C for 30 min in Krebs-Henseleit bicarbonate buffer (pH 7.4) containing 0, 0.5, 2 and 5 mM glutamine. Oxygen consumption was linear during the 30 min incubation period. The rates of citrulline synthesis were low or negligible in enterocytes from 14-21-day-old pigs, but increased 10-20-fold in the cells from 29-58-day-old pigs. This marked elevation of citrulline synthesis coincided with an increase in the activity of pyrroline-5-carboxylate synthase with the animal's post-weaning growth. In contrast, decreases in the activities of phosphate-dependent glutaminase, ornithine aminotransferase, ornithine carbamoyltransferase and carbamoyl-phosphate synthase were observed as the age of the pigs increased. The concentrations of carbamoyl phosphate in enterocytes from pre-weaning pigs were higher than, or similar to, those in the cells from post-weaning pigs. It is possible that the low rate of citrulline synthesis from glutamine in enterocytes from pre-weaning pigs was due to a limited availability of ornithine, rather than that of carbamoyl phosphate. We suggest that this limited availability of ornithine in pre-weaning-pig enterocytes results from (i) the low rate of pyrroline-5-carboxylate synthesis from glutamate, due to the low activity of pyrroline-5-carboxylate synthase, and (ii) the competitive conversion of pyrroline-5-carboxylate into proline. Our present findings on the developmental aspect of citrulline synthesis in pig enterocytes may offer a biochemical mechanism for the previous observations that arginine is a nutritionally essential amino acid for suckling piglets, but not for adult pigs.

The human placenta contains a considerable amount of 1-pyrroline-5-carboxylate dehydrogenase (23 +/- 6 micrograms/g; n = 12), about 25% of the concentration present in liver. The enzyme is the only form in placenta that oxidizes short- and medium-chain aldehydes, which facilitates its purification from this organ. It can be purified to homogeneity by successive chromatographies on DEAE-cellulose, 5′-AMP-Sepharose and Sephacryl S-300. From 500 g of tissue, about 2.1 units of enzyme can be obtained with a 12% yield. Placental 1-pyrroline-5-carboxylate dehydrogenase is a dimer of Mr-63,000 subunits. It exhibits a pI of 6.80-6.65, and is specific for 1-pyrroline-5-carboxylate, the cyclic form of glutamate gamma-semialdehyde (Km = 0.17 mM, kcat. = 870 min-1), although it also oxidizes short-chain aliphatic aldehydes such as propionaldehyde (Km = 24 mM, kcat. = 500 min-1). These properties are very close to those of the liver enzyme, indicating a strong similarity between the enzyme forms from both organs. The enzyme is highly sensitive to temperature, showing 50% inhibition after incubation for 0.8 min at 45 degrees C or after 23 min at 25 degrees C. It is irreversibly inhibited by disulfiram, and a molar ratio inhibitor: enzyme of 60:1 produced 50% inhibition after incubation for 10 min. A subcellular-distribution study indicates that the enzyme is located in two compartments: the mitochondria, with 60% of the total activity, and the cytosol, with 40% activity. The physiological role of the enzyme in placental amino acid metabolism is discussed.

La proline, acide aminé protéinogène, joue un rôle crucial dans le métabolisme cellulaire. Dans les mitochondries, la proline est oxydée en glutamate par l'action séquentielle de la proline déshydrogénase (ProDH) et de la pyrroline-5-carboxylate (P5C) déshydrogénase (P5CDH). L'ornithine-δ-aminotransférase (δOAT) participe également à la formation de P5C via la conversion de l'ornithine et de l’α -cétoglutarate en glutamate et P5C. L’utilisation de mutants et d’approches biochimiques a révélé que ProDH1, P5CDH et δOAT sont impliquées dans la sénescence des feuilles induite à l'obscurité (DIS) chez Arabidopsis thaliana. Une accumulation importante de P5C et de proline est observée chez le mutant p5cdh et, dans une moindre mesure chez le mutant prodh1prodh2, suggérant un cycle proline-P5C. Les mutants prodh1prodh2 et p5cdh ont un profil métabolomique similaire qui diffère de celui du WT et de oat, démontrant ainsi le rôle de l'oxydation de la proline au cours de la sénescence. Nous avons montré que ProDH1 est essentiellement associée à la membrane mitochondriale, tandis que P5CDH et δOAT sont plus uniformément réparties entre la matrice et la membrane. L’oligomérisation de ProDH1, P5CDH et δOAT a été révélée à l'aide d’une analyse de complémentation bimoléculaire de fluorescence (BiFC). Les interactions entre ces enzymes du métabolisme du P5C ont été confirmées par des approches de protéomique couplée à la MS en condition de sénescence chez A. thaliana. Ces trois enzymes forment un(des) complexe(s) impliqué(s) dans l'oxydation de la proline pour alimenter la chaîne de transfert d'électrons mitochondriale afin de pourvoir aux besoins énergétiques des cellules sénescentes
The proteinogenic amino acid proline plays a crucial role for cellular metabolism in living organisms. In mitochondria, proline is oxidized to glutamate by the sequential action of proline dehydrogenase (ProDH) and pyrroline-5-carboxylate (P5C) dehydrogenase (P5CDH). In addition, ornithine δ-aminotransferase (δOAT) also participates in P5C formation through the conversion of ornithine and α-ketoglutarate into glutamate and P5C. Using mutants and biochemical approaches, ProDH1, P5CDH and δOAT were shown to be involved during dark-induced leaf senescence (DIS) in Arabidopsis thaliana. Striking accumulation of P5C and proline was observed in p5cdh mutant and to a lesser extent in prodh1prodh2 mutant, suggesting a putative proline-P5C cycle. Metabolomic analysis indicated that prodh1prodh2 and p5cdh have a similar metabolomic profile, but significantly different from wild-type and oat mutant, demonstrating the role of proline oxidation during DIS. ProDH1 was shown to be preferentially associated to the mitochondrial membrane fraction, while P5CDH and δOAT are more evenly distributed between matrix and membrane fractions. Homo- and hetero-oligomerizations of ProDH1, P5CDH, and δOAT were revealed using Bimolecular Fluorescence Complementation (BiFC) assay of infiltrated tobacco leaves. Interactions between P5C metabolism enzymes were further highlighted in DIS leaves using proteomics approaches coupled with mass spectrometry. Our work demonstrates that these three enzymes form P5C metabolic complex(es) involved in the oxidation of proline to fuel mitochondrial electron transfer chain to support the energy needs of senescent cells

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Chagas Disease is a sickness that affects the population present of Latin America and it is classified by the World Health Organization as a Neglected Tropical Diseases. Chagas disease is caused by the flagellated parasite Trypanosoma cruzi, which belong to the same family as Trypanosoma brucei and Leishmania sp., and has a complex life cycle, going from an invertebrate host to a vertebrate one. In order to survive and proliferate in these host changes, T. cruzi must adapt itself to osmotic and oxidative stresses, changes in the environmental ion composition and shifts in energy sources. To perform this adaptation, the amino acid Lproline has presented an important and essential participation that affects the protozoan life cycle, such as support of the mitochondrial metabolism, the host-cell invasion and metacyclogenesis. T. cruzi 1-Delta-Pyrroline-5-Carboxylate Dehydrogenase (TcP5CDH) is involved in the catabolism of proline holding a major role in its conversion by transforming pyrroline-5-carboxylate into L-glutamate (the second step of the catabolic path) and, thus, seeming to be a promising molecular target for new drug development. The amino acids sequence of PP5CDH was used for conservation analysis, secondary structure prediction, identification of functional domains, and building of tertiary structure computer models with the techniques of Molecular Modeling and Molecular Docking. The TcP5CDH (MW: 60 kDa) was expressed in a heterologous fashion in Escherichia coli, and purified with affinity and size exclusion chromatography, resulting in approximately 2 mg/L of expression. The Dynamic Light Scattering assays where carried out with the recombinant P5CDH in the concentrations of 0.5, 1.0, 1.5 e 2.0 mg/mL, and presented an apparent molecular weight of 223,4 kDa (Rh: 12,01 nm), 246,4 kDa (Rh: 12,53 nm), 310,5 kDa (Rh: 13,83 nm) e 312,0 kDa (Rh: 12,13,86 nm), respespectively. The Circular Dichroism spectroscopy was performed with 0.2 mg/mL of TcP5CDH in the presence and absence of 100 μM of NAD+, L-Glu, and its inhibitor Disulfiram, presenting a Tm of Tm 60,01 ºC, 59,76 ºC, 57,76 ºC e 58,18 ºC, showing that TcP5CDH has a more thermic stability without ligands. Also, a deconvolution was made showing that TcP5CDH has 23% of alfa-helix, 12,3% of antiparallel beta-sheetst and 12,4% parallel beta-sheets, 18,3% of turns 41,7% of disorganized structures. These results will contribute to the understanding of the pathway of L- proline in T. cruzi and the possible future development of new drugs.
A Doença de Chagas é uma enfermidade que afeta a população presente nos países da América Latina e é classificado pela Organização Mundial da Saúde como uma Doença Tropical Negligenciada. A Doença de Chagas é causada pelo parasita flagelado Trypanosoma cruzi, pertencente à mesma família dos parasitas Trypanosoma brucei e a Leishmania sp., organismo que possui um complexo ciclo de vida, passando de um hospedeiro invertebrado para um vertebrado. Para sobreviver e proliferar nessa mudança de hospedeiro, o T. cruzi precisa se adaptar a estresses oxido-redutivos e osmóticos, mudanças da composição iônica do ambiente e mudanças na fonte de energia. Para realizar essas mudanças, o aminoácido Lprolina apresenta uma importante participação que afeta o ciclo de vida do parasita como suporte no metabolismo mitocondrial, invasão de células hospedeiras e na metaciclogênese. A 1-Delta-Pyrrolina-5-Carboxilato Desidrogenase de T. cruzi (TcP5CDH) está envolvida no catabolismo da prolina tendo um papel importante na sua conversão através da transformação da pirroline-5-carboxilato em L-glutamato (a segunda etapa da via) e, assim, parece ser um alvo molecular promissor para desenvolvimento de novos fármacos. A sequência de aminoácidos da P5CDH foi utilizada para análises de conservação, predição de estruturas secundárias, identificação de domínios funcionais e modelos computacionais da estrutura terciária através da técnicas de Modelagem por Homologia e Ancoramento Molecular. A TcP5CDH (MW: 60 kDa) foi expressa de forma heteróloga em Eschericia coli, purificada por cromatografia de afinidade e cromatografia de exclusão molecular e, em seguida, concentrada, resultando em aproximadamente 2 mg/L de expressão. Os experimentos de Espalhamento Dinâmico da Luz foram realizados com a P5CDH recombinante nas concentrações de 0.5, 1.0, 1.5 e 2.0 mg/mL e apresentaram uma massa molecular aparente de 223,4 kDa (Rh: 12,01 nm), 246,4 kDa (Rh: 12,53 nm), 310,5 kDa (Rh: 13,83 nm) e 312,0 kDa (Rh: 12,13,86 nm), respectivamente. A Espectroscopia de Dicroísmo Circular foi realizado utilizando 0,2 mg/mL da TcP5CDH e com a proteína na presença de 100 μM de NAD+, L-Glu e do inibidor Dissulfiram, apresentando uma Tm 60,01 ºC, 59,76 ºC, 57,76 ºC e 58,18 ºC, respectivamente. Além disso, uma deconvolução foi realizada mostrando que a TcP5CDH possui 23% de alfa-hélices, 12,3% de folhas-beta antiparalelas, 12.4% de folhas-beta paralelas, 18,3% de voltas e 41,7% de regiões desorganizadas Estes resultados irão contribuir no entendimento da via da L-prolina em T. cruzi e no possível desenvolvimento futuro de novos fármacos.

碩士
國立臺灣海洋大學
生物科技研究所
101
1-pyrroline-5-carboxylate dehydrogenase (P5CD; EC 1.5.1.12) belongs to family IV of aldehyde dehydrogenase, a mitochondrial matrix NAD+-dependent. In metabloism, ornithine of the products of the urea cycle, is converted into proline and 1-pyrroline-5-carboxylate (P5C), then catalyze the oxidation of P5C to glutamate by P5CD. A cDNA encoding 1-pyrroline-5-carboxylate dehydrogenase from Taiwanofungus camphorata (formerly named Antrodia camphorata) was cloned by PCR (TcP5CD). It contains an open reading frame of 1,641 bp which encodes a protein of 547 amino acid residues, molecular mass is 59.4 kDa. To characterize the TcP5CD protein, the coding region was subcloned into both, an expression vector pET-20b(+) transformed into E. coli Rosetta (DE3). The recombinant His6-tag TcP5CD was expressed and purified by Ni2+-nitrilotriacetic acid agarose. The purified enzyme showed bands on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The Michaelis constant (KM) value for 3,5-dimethoxybenzaldehyde with NAD+ and NADP+ were 0.557 mM and 3.93mM. Half-life of the enzyme at 45C was 4.4 min, and its thermal inactivation rate constant kd was 1.23 x 10-2 min-1. The enzyme was most active at pH 7.0. The enzyme’s preferred substrate is veratraldehyde. Other aldehydes can be used as substrates including acetaldehyde, propionaldehyde and veratraldehyde.

碩士
國立屏東科技大學
食品科學系所
95
2-Acetyl-1-Pyrroline (2-AP) was a major flavor component in aromatic rice varieties Tainung 71(Yihchaun Aromatic Rice) and Tainung 72. The qualitative analysis of 2-AP was by GC-MS and found the retention time of 2-AP was approximately at 7.5 minutes. The quantity analysis of 2-AP was also performed by GC-MS. Aromatic 2-AP of Tainung 71 and Tainung 72 were 0.18 ppm and 0.34 ppm, respectively. Results of tracer experiments indicated that the pyrroline source of 2-AP was proline and glutamate, whereas the source of acetyl group was unknown. The hypothesis that 2-AP was synthesized from △1-pyrroline-5 -carboxylate (P5C) and methylglyoxal (MG) was demonstated in vitro. Proline is synthesized from glutamate via the intermediate 1-pyrroline-5-carboxylate (P5C). The intermediate P5C formation for proline synthesis is catalyzed by 1-pyrroline-5-carboxylate synthetase (P5CS). There are two kinds of P5CS which are encoded by OsP5CS1 and OsP5CS2. OsP5CS1 is a housekeeping gene, which supplies proline to the cell, and OsP5CS2 is primarily responsible for stress responses. In this study, OsP5CS1 and OsP5CS2 have been cloned from callus of non-aromatic rice (Tainung 67) and fragrant rice (Tainung 71 and 72) using PCR. The mRNA expression profiles of the OsP5CS1 and OsP5CS2 in the three cultivars were performed by RT-PCR. The results were supported by the quantition of MG and P5C by HPLC. It showed that the transcription levels of OsP5CS2 and the concentrations of MG and P5C in fragrant rice, Tainung 71 and 72, were significantly higher than those in Tainung 67. Therefore, our results indicate that the amount of 2-AP and the quantition of P5C and MG in rice callus have positive correlation.

In Arabidopsis thaliana (L.) Heyhn, the size of the pool of free proline increases up to 27-fold in response to osmotic stress. The magnitude of this accumulation is dependent upon the rate of imposition of the stress. Numerous reports have suggested a role for proline accumulation as a general adaptation to environmental stress. However, controversy surrounds the beneficial effect of proline accumulation in plants under adverse environmental conditions. Stress-induced proline accumulation in plants occurs mainly by de novo synthesis from glutamate. The final and only committed step of proline biosynthesis in plants is catalysed by Δ¹-pyrroline-5-carboxylate reductase (P5CR). The sequence of an incomplete 999 bp cDNA encoding P5CR from A. thaliana was determined. This enabled a preliminary molecular study of the structure and function of both the gene and the corresponding enzyme. The 999 bp cDNA insert in the clone Y AP057 was sequenced on the sense and antisense strands following subcloning of four sub-fragments in appropriate orientations. Comparison with known plant P5CR sequences revealed that Y AP057 does not encode the first 23 N-terminal amino acids of P5CR from Arabidopsis. However, it does encode the remaining 253 amino acid residues of Arabidopsis P5CR The cDNA Y AP057 is complete on the 3' end as indicated by the presence of a poly(A) tail. The nucleotide sequence determined shows complete homology to the corresponding exons of the genomic copy of a bona fide gene encoding P5CR in A. thaliana (Verbruggen et al, 1993). The only difference observed between the sequence of Y AP057 and that of a cDNA sequenced by these workers is that polyadenylation was initiated seven nucleotides earlier in Y AP057 than in the sequence of the published cDNA. Genomic Southern analysis suggests the presence of only a single copy of the gene encoding P5CR in Arabidopsis. Restriction mapping and sequencing the ends of another incomplete Arabidopsis P5CR cDNA clone FAFJ25 (664 bp) indicated that the regions sequenced were completely homologous to the corresponding portions of Y AP057. Analysis of codon usage in the Arabidopsis gene encoding P5CR revealed it to closely resemble the consensus pattern of codon usage in A. thaliana. This suggests that the gene is moderately. expressed. Expression of the gene encoding P5CR in Arabidopsis is not likely to be subject to translational control. Although P5CR from A. thaliana has a fairly high composition of hydrophobic amino acid residues, it does not possess any stretches of hydrophobic amino acids of sufficient length to act as membrane-spanning domains or to anchor the enzyme in a membrane. Neither does it contain an N- terminal leader sequence capable of directing it to either the plastid or mitochondrion. The enzyme therefore appears to be cytosolic. The nucleic acid and deduced amino acid sequences of Arabidopsis P5CR were compared with those from·eleven other organisms for which P5CR sequences are currently available. Except among the three different plants examined, P5CR sequences displayed less identity at the amino acid level than at the nucleotide level. The deduced amino acid sequence of Arabidopsis P5CR exhibits high similarity to the corresponding genes and amino acid sequences of P5CR from soybean and pea. Lower but significant similarity was observed to the amino acid sequences of P5CRs from human, Saccharomyces cerevisiae and the bacteria Escherichia coli, Pseudomonas aeruginosa, Thermus thermophilus, Mycobacterium leprae; Treponema pallidum and Methanobrevibacter smithii. Similarity was also observed to the translational product of a gene from Bacillus subtilis with high homology to the E. coli proC gene. However, construction of a phenogram indicating the relatedness of the various P5CR enzymes suggests that sequence analysis of this enzyme is not a good indicator of evolutionary relatedness of organisms from different biological kingdoms. Multiple alignment of the twelve known P5CR sequences indicated homology between the sequences across their entire lengths. Homology was particularly high in the C-terminal portions of the P5CRs studied. It is speculated that this region may be of importance in binding of the substrate Δ¹-pyrroline-S-carboxylate (P5C). Another region displaying high sequence conservation was found in the central portion of all P5CRs. All P5CRs studied, with the exception of PSCR from T. pallidum contained an N-terminal domain capable of binding a nicotinamide dinucleotide cofactor. Comparison of this region with consensus sequences for NADH and NADPH binding sites in proteins suggests that NADPH is the preferred reductant used by P5CRs from plants and human. In contrast, the N-terrninal domains of P5CRs from S. cerevisiae, M smithii, T. thermophilus and M leprae display greater similarity to a consensus NADH-binding site. The definite preference of plant P5CRs for NADPH in comparison with NADH suggests that P5CR may be involved in regulating the redox potential within plant cells and that this step in proline biosynthesis from glutamate may be of importance in overall metabolic regulation. Three amino acid residues are universally conserved in all P5CRs studied. All are found within blocks of high sequence similarity. These residues are likely to be of importance in the structure or catalytic mechanism of P5CR. A number of other residues are common to several of the enzymes examined. These may also be of importance in subsequent manipulation of Arabidopsis P5CR at the molecular level. Prediction of the putative secondary structures of A. thaliana, soybean, pea, human and E. coli indicated a high degree of similarity between the enzymes. This was particularly evident in the region of the putative P5C-binding domain. Considerable similarity exists in hydrophobicity profiles of P5CRs from these five organisms. Proline levels in reproductive organs of unstressed Arahidopsis plants were considerably higher than those in vegetative tissues. This suggests differential expression of enzymes involved in proline metabolism in these organs. In situ hybridisation studies indicated an increase in levels of mRNA transcripts encoding P5CR in stem tissues in response to water deprivation stress. Regulation of levels of mRNA transcript encoding P5CR in Arabidopsis therefore appears to be an osmotically sensitive process. Furthermore, this accumulation of transcript occurred in a tissue-specific manner. In particular, an increase in levels of transcript encoding P5CR was observed in the cortical parenchyma, phloem, vascular cambium and pith parenchyma in the vicinity of the protoxylem. The significance of these findings in contributing to a better understanding of the role of proline in adaptation to environmental stress is discussed.
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

AbstractDomestic dogsand cats have evolved differentially in some aspects of nutrition, metabolism, chemical sensing, and feedingbehavior. The dogs have adapted to omnivorous dietscontaining taurine-abundant meat and starch-rich plant ingredients. By contrast, domestic catsmust consumeanimal-sourced foodsfor survival, growth, and development. Both dogsand catssynthesize vitamin C and many amino acids (AAs, such as alanine, asparagine, aspartate, glutamate, glutamine, glycine, proline, and serine), but have a limited ability to form de novo arginineand vitamin D3. Compared with dogs, cats have greater endogenousnitrogen losses and higher dietary requirements for AAs (particularly arginine, taurine, and tyrosine), B-complex vitamins (niacin, thiamin, folate, and biotin), and choline; exhibit greater rates of gluconeogenesis; are less sensitive to AA imbalances and antagonism; are more capable of concentrating urine through renal reabsorption of water; and cannot tolerate high levels of dietary starch due to limited pancreatic α-amylase activity. In addition, dogs can form sufficient taurinefrom cysteine(for most breeds); arachidonic acidfrom linoleic acid; eicosapentaenoic acid and docosahexaenoic acid from α-linolenic acid; all-trans-retinol from β-carotene; and niacinfrom tryptophan. These synthetic pathways, however, are either absent or limited in all cats due to (a) no or low activities of key enzymes (including pyrroline-5-carboxylate synthase, cysteinedioxygenase, ∆6-desaturase, β-carotene dioxygenase, and quinolinate phosphoribosyltransferase) and (b) diversion of intermediates to other metabolic pathways. Dogs can thrive on one large meal daily, select high-fat over low-fat diets, and consume sweet substances. By contrast, cats eat more frequently during light and dark periods, select high-protein over low-protein diets, refuse dryfood, enjoy a consistent diet, and cannot taste sweetness. This knowledge guides the feeding and care of dogsand cats, as well as the manufacturing of their foods. As abundant sources of essentialnutrients, animal-derivedfoodstuffs play important roles in optimizing the growth, development, and health of the companionanimals.

Abstract Deficiency of the mitochondrial matrix protein ornithine aminotransferase (OAT; L-ornithine:2-oxoacid aminotransferase; EC 2.6.1.13) causes gyrate atrophy of the choroid and retina, an autosomal recessive, blinding human disease. The enzyme catalyzes the interconversion of ornithine and a-ketoglutarate to pyrroline 5’ carboxylate and glutamate (3). OAT synthesis is controlled posttranscriptionally by a regulatory system which also controls light/dark cycles of protein synthesis. OAT increases in presence of a high protein diet, and is affected by glucagon and glucocorticoid levels. A variant protein has been recovered from offspring of a male mouse treated with ethylnitrosourea that co-migrates with purified mouse liver OAT, binds anti-rat-OAT antibodies, increases in mice fed a high protein diet, and can be purified usmg an OAT purification procedure.