The response of three amino acid biosynthetic enzymes, threonine dehydratase, tyrosine aminotransferase and saccharopine dehydrogenase, to conditions of histidine, tryptophan or lysine limitation was investigated in 15 yeast species. The activities of all these enzymes increased about two- to fourfold as a result of action of the general control of amino acid biosynthesis in Brettanomyces anomalus, Candida maltosa, Hansenula polymorpha, Rhodosporidium toruloides, Saccharomyces cerevisiae and Yarrowia lipolytica. No evidence for the existence of the general control was found in Candida brumptii, Candida utilis, Hansenula anomala, Hansenula henricii, Kluyveromyces marxianus, Pichia guilliermondii, Saccharomycopsis capsularis, Trichosporon adeninovorans and Trigonopsis variabilis.

28 yeast strains comprising a number of genera and species have been studied with respect to their ability to use L-lysine as carbon or nitrogen source. Based on the utilization of this amino acid we could separate the yeasts into 3 groups. Enzymatic investigations demonstrate that yeasts can degrade L-lysine by two distinct pathways. The first step of both ways was investigated and it was demonstrated that 3 enzymes, acetyl-CoA : L-lysine N-acetyltrdnSferdSe, L-lysine e-aminotransferase, L-lysine Edehydrogenase, are able to catalyze the initial reaction. In 9 yeast strains the acetyltransferase was found. In 21 strains the aminotransferase and in 2 species the dehydrogenage could be detected. The enzyme formation could be enhanced in cells grown in the presence of L-lysine as sole carbon and/or as sole nitrogen source.Both the biosynthesis and the catabolism of L-lysine show considerable variation from one life form to another. No fewer than 8 distinct catabolic routes for this amino acid have been proposed for animals, fungi and bacteria. The initial steps are the following reactions :

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L-Lysine:2-oxoglutarate 6-aminotransferase (EC 2.1.6.36) was purified 202-fold from the yeast Candida utilis. The subunit Mr estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis was 40 kDa. The Mr of the native enzyme was estimated to be 83 kDa by gel filtration, suggesting a dimeric structure. The enzyme exhibits absorption maxima at 280, 340 and 420 nm, and binds 2 mol pyridoxal-5-phosphate/mol of the native enzyme. The aminotransferase has a maximum activity at pH 8.5 and at 4 degrees C. 2-Oxoglutarate is the best amino acceptor with L-lysine as amino donor. Lower activity is observed with oxaloacetate (38%), pyruvate (19%) and 2-oxoadipate (7%) as acceptor or with L-thialysine (13%) as donor. The Km values are 2.5 mM for L-lysine, 3.8 mM for 2-oxoglutarate and 0.015 mM for pyridoxal-5-phosphate. The enzyme activity is induced in cells grown in the presence of L-lysine.

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