The intracellular α-aminoadipic acid pool in Streptomyces glavuligerus mycelium growing in a starch-peptone medium decreased during the late exponential and stationary phases when cephamycin was being produced; however, the amino acid accumulated extracellularly. Although the specific activity of lysine ɛ-aminotransferase (LAT) decreased during this period, there was no indication that the extracellular α-aminoadipic acid functioned as a precursor reserve for synthesis of the β-lactam antibiotic. Measurement of LAT activity in cultures grown in defined media with starch and various nitrogen sources indicated that the enzyme was synthesized preferentially only during early growth. In its insensitivity to induction by a precursor, and in its susceptibility to carbon catabolite repression, LAT behaved as a secondary metabolic pathway enzyme. Unexpectedly, however, the enzyme increased in specific activity when cultures were supplemented with excess phosphate. Unlike LAT, cadeverine aminotransferase was inducible by lysine or cadaverine and insensitive to phosphate; its features were consistent with a role in the catabolism of lysine by S. clavuligerus.