D-glyceraldehyde-3-phosphate dehydrogenase: pre-existent asymmetry of the tetramer and its functional implications.

Modification of a single arginine residue per subunit of rabbit muscle D-glyceraldehyde-3-phosphate dehydrogenase stabilizes the tetramer in a conformation wherein only two active sites are capable of performing catalysis (oxidation of D-glyceraldehyde 3-phosphate or hydrolysis of p-nitrophenyl acetate). The modified enzyme exhibits half-of-the sites reactivity towards iodoacetate and iodoacetamide, known to be 'all-of-the-sites reagents' with the native enzyme. Evidence is presented supporting the model of a built-in asymmetry of the tetramer. The results obtained suggest that the arginine residue (probably Arg-231) controls the conformational transition between the asymmetric and symmetric states of the tetramer.