[Reaction of apo-aspartate aminotransferase with 5-thiophosphate analogues of the coenzyme. Split of the thiophosphate bond].

By the interaction of pyridoxamine- and pyridoxale-5'-thiophosphate with aspartate-aminotransferase complexes similar in their properties to corresponding forms of the native enzyme were obtained. Reversible convertions of the obtained complexes were performed by short time incubation with substrates. It was found that the thioester bond can be splitted as a result of incubation of the pyridoxamine-5'-thiophosphate form of the enzyme with the substrate mixture for several hours at pH 5.0. The same split took place during incubations of the complex of apo-enzyme with L-Nalpha-(pyridoxyl-5'-thiophosphate)-glutamic acid at pH 3.5 within several minutes. The split of the thioester bond was accomplished by formation of phosphate-enzyme bonds, the latter was found to be stable towards gel-filtration and denaturation, but unstable to proteolysis. The labilisation of the thiophosphate bond was explained in terms of changes of structure and specificity of the anchoring site of 5'-phosphoryl group according to the reaction coordinate.