Chicken liver phosphofructokinase. I. Crystallization and physicochemical properties

Chicken liver and breast muscle phosphofructokinases were purified to homogeneity; the liver enzyme was crystallized. The liver phosphofructokinase is reversibly inactivated at low temperatures. This property appears to be unique to phosphofructokinases from avian livers; the enzyme from other tissues of chicken and from the livers of several other animals are stable in the cold. Sucrose density gradient centrifugation, gel filtration, and ultracentrifugal analysis reveal polymeric forms of the chicken liver enzyme, with the distribution depending upon the conditions and protein concentration. The molecular weight of the monomeric form of the liver enzyme is approximately 400,000. However, the enzyme in NaHCO₃ at pH 10.5 has a molecular weight of about 210,000. In 7 M guanidine hydrochloride the enzyme dissociates into subunits of 60,000 ± 5,000 daltons. Peptide mapping and gel electrophoresis in sodium dodecyl sulfate suggest that these subunits are identical. Negative stain electron microscopy indicates that stable dimers and tetramers are formed by self association of these subunits. Under appropriate conditions, the higher polymeric forms result from aggregation of the tetramers into chains or sheets.