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

AbstractPyrophosphate-dependent 6-phosphofructo-1-phosphotransferase (PFP) consists of α (regulatory) and β (catalytic) subunits. The α-subunit was previously reported to be much more susceptible to tryptic digestion than the β-subunit. In this study, ligand-induced protection of PFP subunits against proteolysis by subtilisin was investigated in vitro and the data obtained demonstrated that fructose 1,6-bisphosphate (Fru-1,6-P2), while exerting negligible effect on the β-subunit, remarkably protected the α-subunit against proteolytic degradation. Western blot analysis revealed a good correlation between the Fru-1,6-P2 concentration and the degree of corresponding protection on the α-subunit against proteolysis. In contrast, none of other examined ligands including fructose 2,6-bisphosphate, fructose 6-phosphate and pyrophosphate had such protection on the α-subunit. This finding (1) indicates that the stability of the α-subunit can be selectively increased by Fru-1,6-P2, and (2) suggests that Fru-1,6-P2 is likely a special effector of the α-subunit