Purification and some properties of phosphomannomutase from corms of Amorphophallus konjac C. Koch

Phosphomannomutase [Glazer et al.: Biochim. Biophys. Acta 33:522–625 (1959)] was purified 1700-fold in a 39% yieldfrom cell-free extract of konjak (Amorphophallus konjac C. Koch)corms. The molecular weight of the enzyme as determined by gelfiltration was about 62,000. The enzyme required both Mg²+ and-D-glucose-l,6-bisphosphate for activity, although Mg²+ waspartially replaceable by either Co²+ or Ni²+. An apparent equilibriumconstant, K_eq=(mannose-6-phosphate) (mannose-1-phosphate), wasdetermined to be 8.5. Activity was maximal at pH 6.5 to 7.0.Activation energy was 11.1 kcal/mole. The enzyme was the moststable at pH 7.5. The addition of substrate or cofactor markedlyincreased enzyme stability toward heat denaturation. The enzymewas more labile to heat than phosphoglucomutase from konjakcorms. Treatment with various metal ions in Tris buffer inhibited theenzyme. Cu²+ and Zn²+ were the most potent inhibitors amongthe metal ions tested, while Co²+ and Ni²+ were weak. When theenzyme was treated with metal ions in the presence of histidinebuffer, Cu²+ and Zn²+ showed no inhibitory effect on the enzyme,whereas Be²+ inhibited it to an extent similar to that in Trisbuffer. Plots of 1/v versus l/(mannose-l-phosphate) at different fixedconcentrations of glucose-1,6-bisphosphate and 1/v versus 1/(glucose-1,6-bisphosphate)at different fixed concentrations of mannose-1-phosphate wereseries of converging lines. Mannose-1-phosphate at high concentrationswas found to inhibit the enzyme competitively with respect toglucose-l,6-bisphosphate. Apparent K_m and K₁ values for mannose-1-phosphatewere calculated to be 0.2 mM and 1.2 mM, respectively. The K_mvalue for glucose-1,6-bisphosphate was 1.8 µM. ¹This paper constitutes part 5 of a series of studies on konjakmannan biosynthesis. (Received May 24, 1976; )