Phosphate-dependent glutaminase (PDG) was measured in kidney cortex homogenates and mitochondria from control and acutely acidotic rats. The effect of plasma from acutely acidotic rats on PDG activity in homogenates from normal rats was also studied. Acidosis or incubation in acidotic plasma enhanced enzyme activity when measured at 1.0 mM but not at 20.0 mM glutamine. This effect was not due to increased mitochondrial permeability since similar results were obtained after solubilization of the enzyme with Triton X-100. Increased enzyme activity was observed with either the Tris (monomer) form or the borate (polymer) form of the enzyme, indicating that enhanced activity is not due to polymerization but probably to a conformational change in the enzyme such that the Km for glutamine is lowered.
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