DIVALENT-CATIONS AND CHELATORS AS REGULATORS OF BRAIN FRUCTOSE-1,6-BISPHOSPHATASE

Purified fish and rat brain FruP(2)ase(s) are stimulated by a number o f chelators, viz., histidine, EDTA, citrate, imidazole, and a number o f histidine analogues. These also impart 5'-AMP sensitivity to the oth erwise insensitive enzyme. Beyond 3 mM concentration, histidine inhibi ts the enzyme activity, which can be prevented by Mn2+. Atomic absorpt ion spectrophotometry showed the presence of 5-6 mol of Mn2+ and Zn2bound to both fish and rat brain FruP(2)ase, which can be removed by e xhaustive EDTA-dialysis. The EDTA-dialyzed brain FruP(2)ase records an absolute Mn2+ requirement and 5'-AMP sensitivity without any chelator treatment. The 5'-AMP sensitivity of such enzyme is abolished by prio r incubation with Zn2+. The Zn2+-treated brain FruP(2)ase fails to bin d to a Blue-Sepharose column, in contrast to that seen using the untre ated enzyme. These results suggest that rat and fish brain FruP(2)ase( s) are actually Mn2+- and Zn2+-containing proteins with Zn2+ bound at or near the nucleotide-binding site. (C) 1995 Academic Press, Inc.