Effects of amino acids on transaminase production in Neurospora crassa: evidence for four different enzymes

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Abstract
Addition of certain amino acids to the growth medium of wild-type N. crassa, mating-type A, number 126-1, results in increased concentrations of certain transaminases in mycelial extracts. At least 4 different enzymes must be postulated. The alanine-glutamate transaminase (in the absence of added pyridoxal phosphate) has variable and generally low activity, and its production is not markedly affected by exogenous amino acids. The aspartate-glutamate transaminase generally showed rather high activity which was not consistently affected by added amino acids. The ornithin-glutamate transaminase activity appears to be stimulated 2- to 3-fold by a variety of amino acids including arginine. Nine other transaminase activities appeared to be correlated and may be properties of a single enzyme which is capable of catalysing glutamate formation from phenylalanine, isoleucine, valine, leucine, norleucine, norvaline, methionine, [alpha]-amino-butyric acid and tryptophan, in decreasing order of activity. The production of this enzyme, or correlated group of enzymes, is increased usually at least 5-fold by the presence in the medium of valine, leucine, isoleucine, phenylalanine or methionine. Activities of both the alanine-glutamate transaminase and the transaminase referred to in (5) were stimulated by fortification of the reaction mixture with pyridoxal phosphate. The other 2 enzymes showed no response to pyridoxal phosphate.