THREONINE DEAMINATION IN ESCHERICHIA COLI I

Abstract

Deamination reactions of L- and D-threonine by cell-free extracts of Escherichia coli are stimulated by pyridoxal phosphate. D-threonine is probably deaminated by the D-serine dehydrase of Metzler and Snell. Very little fluctuation in the amount of these activities was noted with various growth conditions. L-Threonine dehydrase activity is absent from cells in stationary phase cultures which contained excess glucose. Evidence was obtained which indicates this glucose effect is due to accumulation of acidic products and occurs only after growth has ceased. The finding that L-threonine dehydrase activity is always present in growing cells suggests that this step may be of importance in biosynthesis of isoleucine. It is concluded that D-threonine dehydrase is responsible for slow growth of certain isoleucineless mutants of E. coli on this compound.