TARGETING OF THE CATALYTIC SUBUNIT OF PROTEIN PHOSPHATASE-1 TO THE GLYCOLYTIC ENZYME PHOSPHOFRUCTOKINASE

In this study, we demonstrate that the catalytic subunit of rabbit mus cle protein phosphatase-1 (PP1) binds to muscle phosphofructokinase (6 -phosphofructo-1-kinase, PFK). A protein of 85 kDa was isolated from r at muscle by affinity chromatography on PP1-Sepharose and was identifi ed as phosphofructokinase by partial amino acid sequence analysis. Thi s novel finding of a protein-protein interaction between PP1 and PFK w as confirmed by reciprocal experiments in which the binding of PP1 to PFK-agarose was demonstrated. Elution of PP1 from PFK-agarose was maxi mal at ca. 0.4 M NaCl. The specificity of binding was demonstrated by isolation of PP1 from a partially purified rabbit muscle PP1 preparati on. All four known isoforms of PP1 (PF1 alpha, PP1 gamma 1, PP1 gamma 2, and PP1 delta) were shown to bind to PFK-agarose. The activity of P P1 was only partially inhibited by PFK. The preformed complex between PP1 and PFK did not bind to inhibitor-2-Sepharose. The stoichiometry o f binding of PP1 to the PFK monomer was found to be 1:1 in the isolate d PP1.PFK complex. An interaction between PP1 and PFK in muscle extrac ts was demonstrated by their coimmunoprecipitation. Our findings raise the interesting possibility that PP1 may be targeted to PFK, and may be physiologically relevant in the context that PFK and other glycolyt ic enzymes have been shown to be micra-compartmentalized by binding to F-actin. This in turn points to a role for PP1 in control of glycolyt ic flux by protein phosphorylation-dephosphorylation mechanisms.