The isolation and specific activity of rabbit-muscle glyceraldehyde phosphate dehydrogenase

Abstract

Reported values for the specific activity of glycer- aldehyde phosphate dehydrogenase [D-glycer- aldehyde 3-phosphate-NAD oxidoreductase (phos- phorylating), EC 1.2.1.12] isolated from rabbit skeletal muscle have varied considerably (Table The present investigation was undertaken in an attempt to obtain material of reproducibly high specific activity. The approach to a quick and re- producible method of isolating the enzyme was based on an observation of Smithies (1954). He showed that the composition of a crystalline sample of P-lactoglobulin (containing two or possibly three components) remained unchanged throughout repeated crystallizations owing to the formation of highly stable mixed crystals. He concluded that '. . . crystallisation should be avoided in the further purification of proteins which have already been crystallised once'.