The activation of rabbit muscle, liver, and kidney fructose bisphosphatases by histidine and citrate

Abstract

Purified fructose 1,6-bisphosphatases from rabbit muscle, liver, and kidney require a metal chelator for optimal activity at neutral pH. This requirement is satisfied by physiological concentrations of histidine and citrate, and at pH 7 their effects are additive. In the presence of both histidine and citrate the optimum activity is shifted from about pH 8 to pH 7.2, and the activity is greater than that obtained with optimal concentrations of EDTA. Carnosine, anserine, and 1-methyl histidine are also effective, but only at much higher concentrations, while 3-methyl histidine is effective in the same concentration range as is histidine. Isocitrate can replace citrate. The results suggest that fructose bisphosphatases possess distinct binding sites for divalent cations (Mg²⁺ or Mn²⁺) and also for histidine and citrate complexes of these cations.