Abstract
The transaminations of L-tryptophan (L-trp) and of L-phenylalanine (L-phe) are catalysedin vitro by the same non-specific aminotransferase. The transaminations procceed at the same pH (pH 8.5) and temperature (45 °C) optima, have parallel increases in activity with addition of the coenzyme pyridoxal phosphate (PRP) and have identical elution characteristics in gel chromatography. The enzyme from pea seedlings has a relatively weak affinity for both amino acids (Km L-trp = 4.16 × 10−1 mmol 1−1; Km L-phe = 2.10 × 10−1 mmol 1−1). Differences in affinity for a series of keto acids in the pea enzyme were observed, with pyruvate having the strongest and glyoxylate the weakest affinity. Transamination of L-trp and L-phe was demonstrated by enzyme extracts from pea, maize and tomato, but was not detected in kohlrabi. The amino acids L-asparagine (L-asn), L-phe, L-lysine (L-lys), L-methionine (L-met) have distinct inhibitory effects on the transamination of L-trp. Indolylacetylaspartate and tryptophol were shown to be competitive inhibitors. The regulation at the molecular level of L-trp transaminase activity is discussed.
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Abbreviations
- L-trp:
-
L-tryptophan
- L-phe:
-
L-phenylalanine
- L-asp:
-
L-aspartic acid
- L-lys:
-
L-lysine
- L-met:
-
L-methionine
- PRP:
-
pyridoxal phosphate
- IAA:
-
indoly1-3-acetic acid
- IPyA:
-
indolyl-3-pyruvic acid
- IAAsp:
-
indolylacetylaspartic acid
- ILA:
-
indolyl-3-lactic acid
- IAN:
-
indolyl-3-acetonitrile
- T-NH2 :
-
tryptamine
- PPyA:
-
phenylpyruvic acid
- PyA:
-
pyruvic acid
- KG:
-
α-ketoglutarate
- T-OH:
-
tryptophol
- TAT:
-
L-tryptophan aminotransferase
- PAT:
-
L-phenylalanine aminotransferase
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Terziivanova-Dimova, S.D., Kutáček, M. Enzymes of auxin biosynthesis and their regulation I. Tryptophan and phenylalanine aminotransferase in pea plants. Biol Plant 33, 277–286 (1991). https://doi.org/10.1007/BF02885374
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DOI: https://doi.org/10.1007/BF02885374