Reversible Dissociation of Tetrameric Rabbit Muscle Glyceraldehyde 3-Phosphate Dehydrogenase into Dimers or Monomers by Adenosine Triphosphate

Tetrameric 7.5 S rabbit muscle glyceraldehyde 3-phosphate dehydrogenase is dissociated by ATP at 0° into 4.5 S dimers or 2.8 S monomers, depending upon the protein concentration. Dissociation into two peaks is observed at protein concentrations as high as 10 mg per ml, and a 4.5 S dimer is produced in increasing quantity from the 7.5 S tetramer as the protein concentration is lowered from 10 to 2 mg per ml. At 1 mg per ml, a single 4.2 S dimer peak is observed, and at 0.1 mg per ml, a single 2.8 S monomer peak is observed. Between 1.0 and 0.1 mg per ml, only single peaks with sedimentation coefficients intermediate to those of the dimer and monomer are observed, suggesting a fairly rapidly equilibrating mixture of 2.8 S monomers and 4.5 S dimers in varying amounts. The observed inactivation is only slight at temperatures down to 12°, but the equilibrium is shifted fairly strongly toward inactive subpolymers at 7° and apparently is shifted completely to inactive monomers at 0° at 0.05 mg per ml of enzyme. The dissociation has practically no pH dependence in the range of 6.5 to 9.5, but it is somewhat greater and faster at pH 5.5 than at all others studied. Inactivation and dissociation are reversed by rewarming the enzyme to 23° and removing the ATP. Ammonium sulfate, 1 m , or 2 m m NAD protects against inactivation and dissociation. Dissociation is faster with ATP than with other adenine nucleotides and much faster and more pronounced with ATP than with GTP, UTP, CTP, FAD, and CoA.