Effects of specific antibodies on the catalytic activity of L asparaginase from Serratia marcescens and Escherichia coli

Abstract

Rabbit antisera against highly purified L asparaginase from S. marcescens and from E. coli showed up to 60% inhibition of the catalytic amidohydrolysis of L asparagine when combined with the homologous enzyme. This inhibition was diminished somewhat against the heterologous enzyme. Kinetic studies in the presence of these antisera showed an increased K(m)app for both homologous and heterologous enzymes using L asparagine as substrate. In contrast, kinetic studies employing the poor substrate L glutamine, showed activation attributable to specific antibodies. This was seen in lower K(m)app values and up to twofold increases in the V(max) over the normal rabbit serum controls. The high degree of cross inhibition (80%) and the low degree of cross reactivity in the quantitative precipitin test (34%) suggest that these two enzymes possess structural similarities located mainly in the regions of the catalytic sites.