Lysine is catabolized to 2-aminoadipic acid in <Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> by an omega-aminotransferase and to saccharopine by a lysine 2-ketoglutarate reductase. Characterization of the omega-aminotransferase

The biosynthesis and catabolism of lysine in Penicillium chrysogenum is of great interest because these pathways provide 2-aminoadipic acid, a precursor of the tripeptide δ-L-2-aminoadipyl-L-cysteinyl-D-valine that is an intermediate in penicillin biosynthesis. In vivo conversion of labelled L-lysine into two different intermediates was demonstrated by HPLC analysis of the intracellular amino acid pool. L-lysine is catabolized to 2-aminoadipic acid by an ω-aminotransferase and to saccharopine by a lysine-2-ketoglutarate reductase. In lysine-containing medium both activities were expressed at high levels, but the ω-aminotransferase activity, in particular, decreased sharply when ammonium was used as the nitrogen source. The ω-aminotransferase was partially purified, and found to accept L-lysine, L-ornithine and, to a lesser extent, N-acetyl-L-lysine as amino-group donors. 2-Ketoglutarate, 2-ketoadipate and, to a lesser extent, pyruvate served as amino group acceptors. This pattern suggests that this enzyme, previously designated as a lysine-6-aminotransferase, is actually an ω-aminotransferase. When 2-ketoadipate is used as substrate, the reaction product is 2-aminoadipic acid, which contributes to the pool of this intermediate available for penicillin biosynthesis. The N-terminal end of the purified 45-kDa ω-aminotransferase was sequenced and was found to be similar to the corresponding segment of the OAT1 protein of Emericella (Aspergillus) nidulans. This information was used to clone the gene encoding this enzyme.