Binding of Zn 2+ to rabbit muscle fructose 1,6-bisphosphatase and its effect on the catalytic properties

Abstract

At low concentrations (<1 μM), and in the presence of Mg 2+, Zn 2+ inhibits the activity of rabbit muscle fructose 1,6-bisphosphatase (EC 3.1.3.11). At higher concentrations Zn 2+ can replace Mg 2+ as the activating cation. The inhibitory effects of Zn 2+ are associated with its binding to 4 high-affinity sites (1 per subunit). Binding to a second set of 4 sites requires the presence of the substrate, fructose 1,6-bisphosphate, and binding of Zn 2+ to this set of sites restores the catalytic activity. In the absence of EDTA, Zn 2+ is a better activating cation than Mg 2+. The muscle enzyme differs from rabbit liver fructose 1,6-bisphosphatase in the number of binding sites (8 as compared to 12 for the rabbit liver enzyme) and in showing higher activity with Zn 2+ as the activating cation. The results suggest that Zn 2+ may be the physiological activator.