Purification and characterization of fructose-1,6-bisphosphatase from bovine brain

Fructose-1,6-bisphosphatase from bovine brain tissue has been purified to near homogeneity. This enzyme is similar to other mammalian fructose-1,6-bisphosphatases in many respects, and its properties are distinctly different from those reported for the enzyme from rat brain [A. L. Majumder and F. Eisenberg (1977) Proc. Natl Acad. Sci. USA 74, 3222-3225;S. Chattoraj and A. L. Majumder (1986) Biochem. Biophys. Res. Commun.139, 571-580]. The bovine enzyme (sp act 4, pH ratio ( 7.5 9.6) = 3.6) has a pH optimum of 7.5. The K_m is 2 μm. Divalent metal ion is required for activity, and V_max is obtained at either 4 mm Mg²⁺ or 0.3 mm Mn²⁺. Fructose 2,6-bisphosphate is a competitive inhibitor (K_i = 0.07 μM), and AMP a noncompetitive inhibitor (k_is = 24 μM, K_ii = 10 μM) of bovine brain fructose-1,6-bisphosphatase. The enzyme activity is enhanced by small amounts of EDTA relative to metal, and AMP inhibits fructose-1,6-bisphosphatase in either the presence or absence of the metal chelator; however, AMP is more effective in the absence of EDTA.