Phosphate-activated glutaminase (EC 3.5.1.2; l-glutamine amidohydrolase) purified from pig kidney and brain is activated by CoA and short-chain acyl-CoA derivatives. Acetyl-CoA is the most powerful activator (KA about 0.2mm). Acetyl-CoA is maximally effective in the absence of other activating anions such as phosphate and citrate, and at low glutamine concentrations. The negative co-operative substrate activation observed at pH7 becomes more pronounced in the presence of acetyl-CoA. Similarly to phosphate, acetyl-CoA produces at high protein concentrations a different type of activation, which is time-dependent, depends on protein concentration and is accompanied by an increase in the sedimentation coefficient. Acetyl-CoA, phosphate and citrate appear to have binding sites in common. No significant difference was observed between kidney and brain phosphate-activated glutaminase.
