Isozymes of Rabbit Phosphofructokinase

The distribution of phosphofructokinase isozymes in rabbit tissues was analyzed by electrophoretic and immunochemical techniques. Antisera to the enzyme purified from skeletal muscle and to enzyme purified from liver were prepared. The antiserum to muscle phosphofructokinase showed a partial reaction with the liver enzyme, whereas little cross-reaction was observed with antiserum to liver phosphofructo-kinase toward the muscle enzyme. Skeletal muscle extracts and heart extracts contain a single identical isozyme species. It is proposed that this isozyme be designated phosphofructokinase A. The major isozyme species of liver and erythrocyte are also identical (phosphofructokinase B). All other tissues examined contain isozymes that include both A and B monomers. Extracts of lung, adipose tissue, and stomach contain a complete set of five A-B hybrids. Other tissues appear to contain isozymes that have A and B monomers, but both electrophoresis and antiserum precipitation data indicate that at least one other isozyme is present. This is most obvious in extracts of brain tissue. Electrophoresis of extracts of brain produces at least four activity bands of mobility intermediate between those observed following electrophoresis of isozymes A and B. One of these bands of activity was not removed by treatment with a combination of both antisera while a similar treatment of A-B hybrids removed all activity. The residual activity is designated phosphofructokinase C.