INDUCED FORMATION OF SERINE AND THREONINE DEAMINASES BY ESCHERICHIA COLI

Abstract

D- and L-serine deaminases are inducible enzymes in E. coli. Simple conditions for their formation and assay are described. The same enzyme deamin-ates D-serine and D-threonine. Different enzymes deaminate the L-amino acids, as shown by differential induction. D-serine deammase resembles beta-galactosidase in its mode of induction and properties, but L-serine deaminase differs in many ways. A number of compounds related to serine were tested as inducers. D-serine was the only inducer found for D-serine deaminase, but several compounds, of which threonine, L-leucine, and glycine were the best, induced L-serine deaminase formation. L-threonine deaminase behaved like a constitutive enzyme. The rate of induction of L-serine deaminase was specifically increased by glycine, L-leucine and related compounds. A substrate is not necessarily an inducer in this system; nor need an inducer be a substrate, although inducers generally had an affinity for the enzyme. Implications of the results are discussed.