Purification and Some Properties of Malate Synthase from the Pollen of Pinus densiflora Sieb. et Zucc.

抄録

Malate synthase (EC 4.1.3.2), termed MS_H (mol. wt. 630, 000), was purified from the pollen of Pinus densiflora Sieb. et Zucc. to apparent homogeneity as judged by SDS-PAGE. Part of MS_H was converted to the low molecular weight form of MS, termed MS_L (mol. wt. 62, 000), by incubation with 5 mM ATP. Both forms of MS were maximally active at pH 7.6 in the presence of 10 mM MgCl₂ and 0.01mM EDTA. MS_L was completely inactivated by heating at 50°C for 3min, but MS_H activity was retained about 65%. MS_H preincubated with 5mM ATP showed unstability similar to that of MS_L. MS_H activity was more strongly inhibited than that of MS_L by phosphoenolpyruvate or ATP. Km values of MS_H for acetyl-CoA and glyoxylate were about one half of those of MS_L. The V_max of MS_H was about 5 times as high as that of MS_L. ATP was a noncompetitive inhibitor with respect to acetyl-CoA and Ki values of ATP for MS_H and MS_L were 1.0 × 10^-3 M and 2.0 × 10^-2 M, respectively. From these results we suggested that MS_H and MS_L are the active and low active forms of MS, respectively.