Evidence that fructose 1,6-bisphosphate specifically protects the alpha-subunit of pyrophosphate-dependent 6-phosphofructo-1-phosphotransferase against proteolytic degradation

Pyrophosphate-dependent 6-phosphofructo-1-phosphotransferase (PFP) consists of alpha (regulatory) and beta (catalytic) subunits, The alpha-subunit was previously reported to be much more susceptible to tryptic digestion than the beta-subunit, In this study, ligand-induced protection of PFP subunits against proteolysis by subtilisin was investigated in vitro and the data ob tained demonstrated that fructose 1,6-bisphosphate (Fru-1,6-P-2), while exe rting negligible effect on the beta-subunit, remarkably protected the alpha -subunit against proteolytic degradation, Western blot analysis revealed a good correlation between the Fru-1,6-P-2 concentration and the degree of co rresponding protection on the alpha-subunit against proteolysis, In contras t, none of other examined ligands including fructose 2,6-bisphosphate, fruc tose 6-phosphate and pyrophosphate had such protection on the alpha-subunit , This finding (I) indicates that the stability of the alpha-subunit can be selectively increased by Fru-1,6-P-2, and (2) suggests that Fru-1,6-P-2 is likely a special effector of the alpha-subunit. (C) 1999 Federation of Eur opean Biochemical Societies.