Allosteric properties of a phosphorylase a-glutamic-pyruvic transminase complex

Abstract

A phosphorylase a (EC 2.4.1.1)-glutamic-pyruvic transaminase (EC 2.6.1.2) enzyme complex was purified by DEAE-cellulose and Sephadex gel chromatography. Substrate inhibition studies indicated that the substrates of one enzyme induced conformational changes on the other enzyme in the complex. Iodoacetate alkylation and methylene blue photooxidative destruction as well as substrate protection against these protein modifications provided additional evidence for this. The allosteric effector AMP induces changes in the protein structure of phosphorylase a, which in turn affected the transaminase activity of glutamic-pyruvic transaminase in the enzyme complex.

The AMP effect on the transaminase activity was abolished by raising the temperature of the system or by the addition of urea.

It is believed that the substrate or AMP induced changes in enzymic activity are a result of protein-protein interactions manifesting themselves in a conformational change of phosphorylase a which is communicated to the transaminase enzyme in the complex.