Abstract
Malate synthase (EC 4.1.3.2), termed MSH (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 MSH was converted to the low molecular weight form of MS, termed MSL (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. MSL was completely inactivated by heating at 50°C for 3min, but MSH activity was retained about 65%. MSH preincubated with 5mM ATP showed unstability similar to that of MSL. MSH activity was more strongly inhibited than that of MSL by phosphoenolpyruvate or ATP. Km values of MSH for acetyl-CoA and glyoxylate were about one half of those of MSL. The Vmax of MSH was about 5 times as high as that of MSL. ATP was a noncompetitive inhibitor with respect to acetyl-CoA and Ki values of ATP for MSH and MSL were 1.0 × 10-3 M and 2.0 × 10-2 M, respectively. From these results we suggested that MSH and MSL are the active and low active forms of MS, respectively.
