Penicillanic acid sulfone: an unexpected isotope effect in the interaction of 6.alpha.- and 6.beta.-monodeuterio and of 6,6-dideuterio derivatives with RTEM .beta.-lactamase from Escherichia coli. Crystal structure of penicillanic acid sulfone

Abstract

Penicillanic acid sulfone is both a substrate and an inactivator of the RTEM .beta.-lactamase [of E. coli]. About 7000 hydrolytic events occur before enzyme inactivation. The 6,6-dideuterio sulfone shows a 3-fold acceleration of both the hydrolysis reaction and the enzyme inactivation. The kinetic and spectroscopic results are accommodated by a scheme in which a transiently stable intermediate is formed in an isotopically sensitive step. The deuterated material partitions less readily toward this transiently stable intermediate by virtue of a primary isotope effect, and more enzyme is then available for the hydrolysis and inactivation pathways. Use of the stereospecifically monodeuterated sulfones shows that the 6.beta. hydrogen is preferentially abstracted in the formation of the transiently stable intermediate and allows a detailed picture of the interaction of the sulfone and the .beta.-lactamase to be drawn. The crystal structures of both the labeled and unlabeled compounds are reported.