Degradation of aromatic amino acids in Candida maltosa
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Abstract The degradation of l‐ and d‐aromatic amino acids has been studied in Candida maltosa . The following main metabolites were indentified: indolelactate was the degradation product of tryptophan, phenylpyruvate and phenyllactate were that of phenylalanine and p ‐hydroxyphenylpyruvate and p ‐hydroxyphenyllactate resulted from degradation of tyrosine. The first step of utilization of l‐aromatic amino acids was found to be a transamination. The cells contained increased aromatic aminotransferase activity if grown on medium supplemented with one of the three l‐aromatic amino acids. Three aromatic aminotransferases were separated by DEAE‐cellulose chromatography. The pathway for degradation of d‐aromatic amino acids involves deamination as the initial step. The enzyme was characterized to be a general d‐amino acid oxidase capable of utilizing various d‐amino acids. Synthesis of this enzyme was constitutive. Common products of both enzymatic reactions with the aromatic amino acids were the corresponding aromatic pyruvates. Formation of the aromatic lactate derivatives was catalyzed by an aromatic lactate dehydrogenase. This enzyme possessed a high substrate specificity for p ‐hydroxyphenylpyruvate, phenylpyruvate, and indolepyruvate and was synthesized constitutively.Keywords:
Transamination
Aromatic amine
Deamination
Mimosine
Transamination
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Transamination
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Cytidine
Cytosine
Sodium bisulfite
Bisulfite
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Transamination
Deamination
Transaminase
Ammonia production
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Aromatic L-Amino acids are important chiral building blocks for the synthesis of many drugs, pesticides, fine chemicals and food additives. Due to the high activity and steroselectivity, enzymatic synthesis of chiral building blocks has become the main research direction in asymmetric synthesis field. Guided by the phylogenetic analysis of transaminases from different sources, two representative aromatic transaminases TyrB and Aro8 in type I subfamily, from the prokaryote Escherichia coli and eukaryote Saccharomyces cerevisia, respectively, were applied for the comparative study of asymmetric transamination reaction process and catalytic efficiency of reversely converting keto acids to the corresponding aromatic L-amino acid. Both TyrB and Aro8 could efficiently synthesize the natural aromatic amino acids phenylalanine and tyrosine as well as non-natural amino acid phenylglycine. The chiral HPLC analysis showed the produced amino acids were L-configuration and the e.e value was 100%. L-alanine was the optimal amino donor, and the transaminase TyrB and Aro8 could not use D-amino acids as amino donor. The optimal molar ratio of amino donor (L-alanine) and amino acceptor (aromatic alpha-keto acids) was 4:1. Both of the substituted group on the aromatic ring and the length of fatty acid carbon chain part in the molecular structure of aromatic substrate alpha-keto acid have the significant impact on the enzyme-catalyzed transamination efficiency. In the experiments of preparative-scale transamination synthesis of L-phenylglycine, L-phenylalanine and L-tyrosine, the specific production rate catalyzed by TryB were 0.28 g/(g x h), 0.31 g/(g x h) and 0.60 g/(g x h) and the specific production rate catalyzed by Aro8 were 0.61 g/(g x h), 0.48 g/(g x h) and 0.59 g/(g x h). The results obtained here were useful for applying the transaminases to asymmetric synthesis of L-amino acids by reversing the reaction balance in industry.
Transamination
Alanine
Transaminase
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Abstract The degradation of l‐ and d‐aromatic amino acids has been studied in Candida maltosa . The following main metabolites were indentified: indolelactate was the degradation product of tryptophan, phenylpyruvate and phenyllactate were that of phenylalanine and p ‐hydroxyphenylpyruvate and p ‐hydroxyphenyllactate resulted from degradation of tyrosine. The first step of utilization of l‐aromatic amino acids was found to be a transamination. The cells contained increased aromatic aminotransferase activity if grown on medium supplemented with one of the three l‐aromatic amino acids. Three aromatic aminotransferases were separated by DEAE‐cellulose chromatography. The pathway for degradation of d‐aromatic amino acids involves deamination as the initial step. The enzyme was characterized to be a general d‐amino acid oxidase capable of utilizing various d‐amino acids. Synthesis of this enzyme was constitutive. Common products of both enzymatic reactions with the aromatic amino acids were the corresponding aromatic pyruvates. Formation of the aromatic lactate derivatives was catalyzed by an aromatic lactate dehydrogenase. This enzyme possessed a high substrate specificity for p ‐hydroxyphenylpyruvate, phenylpyruvate, and indolepyruvate and was synthesized constitutively.
Transamination
Aromatic amine
Deamination
Mimosine
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Abstract— Mitochondrial and cytoplasmic forms of aspartate aminotransferase were purified from rat brain homogenates and tested for their ability to catalyze transamination of various aromatic amino acids. The mitochondrial enzyme exhibited activity toward tyrosine and phenylalanine with 2‐oxoglutar‐ate as acceptor, although the specific activities were less than 1% of the corresponding aspartate activity when all substrates were 10 mM. Even less activity was seen with DOPA, 5‐hydroxytryptophan and tryptophan. The cytoplasmic aspartate aminotransferase was active toward tryptophan, 5‐hydroxytryptophan and DOPA, but these transaminations were favored by pyruvate or oxaloacetate rather than 2‐oxoglutarate as keto acid. Based on co‐migration of aromatic activities with the respective aspartate aminotransferases during isoelectric focusing and based on equal sensitivities of aromatic transamination and aspartate transamination to inhibition by vinylglycine, it was concluded that all activities resided in the aspartate aminotransferase enzymes. Some doubt exists, however, as to the physiological significance of these alternate activities in view of the requirement that aromatic amino acids must compete with aspartate for transamination by these enzymes.
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Alanine
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The transamination of aromatic l-amino acids (5-hydroxytryptophan, tryptophan, tyrosine, phenylalanine and kynurenine) was shown to be catalysed by enzyme preparations from rat small intestine. On the basis of the partial purification and characterization of these aromatic amino acid transaminases, it is suggested that rat small intestine contains several kinds of aromatic amino acid transaminases.
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Transamination
Deamination
Cytidine
Bisulfite
Ethylene diamine
Deoxyuridine
Nucleobase
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