ISOLATION AND CHARACTERIZATION OF MANNITOL-1-PHOSPHATE DEHYDROGENASE FROM BROCHOTHRIX THERMOSPHACTA

Abstract

Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17) was purified to homogeneity from anaerobically grown cells of Brochothrix thermosphacta on mannitol. The enzyme was a monomer of apparent molecular weight 50, 000. Reduction of fructose-6-phosphate was optimal at pH 6.5 (K_m Fru-6-p, 0.25mM; V_max, 65 units/mg protein) as compared to a pH maximum of 9.5 for the oxidation of mannitol-1-phosphate (K_m Mno-1-p, 50μM; V_max, 18 units/mg protein). The oxidation reaction was inhibited by ATP and ADP, although these nucleotides had no effect on the reverse reaction. ADP was a stronger inhibitor than ATP (K_i: 0.7 and 1.6mM, respectively). Possible role of this enzyme in maintaining redox balance in this organism is discussed.