Resistance of brain phosphofructo-1-kinase to pH-dependent inhibition.

The kinetic regulatory properties of rabbit brain phosphofructo-1-kinase (PFK), which consists of a mixture of heterotetramers containing A, B, and C isozymic subunits, were found to be much less responsive to pH than the properties of skeletal muscle PFK, the A4 isozyme. The muscle enzyme was strongly inhibited at low pH as a result of a striking increase in the allosteric interaction coefficient or Hill coefficient at pH values below 7.3. This phenomenon was not seen with the brain enzyme. This property of brain PFK may protect this organ, which is exclusively dependent on glucose metabolism, by permitting continued glycolysis despite decreases in intracellular pH.