Rabbit muscle D-Glyceraldehyde-3-phosphate dehydrogenase: Half-of-the-sites reactivity of the enzyme modified at arginine residues

Modification of a single arginine residue per subunit of rabbit muscle apo-D-Glyceraldehyde-3-phosphate dehydrogenase does not affect the rate of hydrolysis of p-nitrophenyl acetate catalyzed by the enzyme, but locks the tetramer in a conformation wherein only two active sites are functioning. The modified enzyme also exhibits half-of-the sites reactivity towards iodoacetate and iodoacetamide. On the other hand, its NAD +-binding characteristics remain unchanged. Evidence is presented supporting the view that mechanisms of half-of-the-sites reactivity and negative cooperativity in coenzyme binding are different. The results are consistent with a built-in asymmetry of the tetramer and suggest that the arginine residue (probably Arg-231) controls the conformational transition between the asymmetric and symmetric states of the tetramer.