Studies on the subunit structure of rabbit liver fructose diphosphatase

Abstract Rabbit liver fructose 1,6-diphosphatase is dissociated in SDS or by treatment with maleic anhydride into two pairs of subunits of different molecular weight. Molecular weight determinations by high-speed sedimentation equilibrium and electrophoresis in polyacrylamide gels yield similar values for the two species, corresponding to 29–31,000 and 35–39,000, respectively. The molecular weight of the native enzyme was found to be 130,700 ± 2,000. The presence of two different peptide chains is supported by hydrazinolysis experiments which yielded nearly two equivalents each of alanine and glycine. Since this enzyme has been shown to bind four equivalents each of substrate and AMP, the species detected in the present experiments may be dimers of catalytic and regulatory subunits, respectively. A new procedure is described for estimating subunit size, based on polyacrylamide gel electrophoresis after treatment of the protein with maleic anhydride.