Role of Histidine 188 in Fructose 1,6-Bisphosphate- and Divalent Cation-Regulated L-Lactate Dehydrogenase of Lactobacillus casei

概要

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A fructose 1, 6-bisphosphate [Fru(1, 6)P_2] and divalent cation-regluated allosteric L-lactate de-hydrogenase (L-LDH) (EC 1. 1. 1. 27) of Lactobacillus casei was highly produced in Escherichia coli cells, together with its mutant enzyme, in which His-188 was replaced by Asp. Under acidic conditions, the mutant enzyme showed positive allosteric regulations by the substrate pyruvate and its analogues, like the wild-type enzyme, but not by Fru(1, 6)P_2, which even inhibited the stimulative effects of the alternative activation factors. In addition, Mn^<2+> ions also showed greatly reduced inhibitory effects on the mutant enzyme. Under neutralconditions, on the other hand, the reaction of the mutant enzyme was slightly enhanced by Fru(1, 6)P_2, but not further stimulated by additional Mn^<2+> ions, unlike the case of the wild-type enzyme. These results indicate that His-188 is, though not essential for the regulation by the alternative factors, essential for the cooperative regulation by Fru(1, 6)P_2 and divalent cations in L. casei L-LDH.
社団法人日本農芸化学会の論文
1995-03-23