Citrate Synthase of Plants: Sensitivity to Sulfhydryl Reagents and Molecular Weight of the Enzyme

Abstract

AbstractCitrate synthase of wheat (Triticum aestivum L.), bean (Phaseolus vulgaris L.), cauliflower (Brassica oleracea L.), and a marine blue‐green alga (Coccochloris elabens) is inhibited by sulfhydryl binding reagents. The inhibitions are partially reversed by dithiothreitol. Pig heart citrate synthase is only slightly inhibited by the same reagents and this is completely reversed by dithiothreitol.All citrate synthases in this study are inhibited by adenosine triphosphate. The inhibition is relieved by increasing the concentration of acetyl coenzyme A.Citrate synthase of wheat, cauliflower, bean, and pig heart was estimated by gel filtration to have a molecular weight of 100,000 daltons. The Coccochloris citrate synthase was estimated to have a molecular weight greater than 250,000 daltons.The evolutionary implications of these findings are discussed.This enzyme is comparable in size to the 100,000 dalton mammalian enzyme (Singh et al. 1970) making it somewhat larger than the 65,000 dalton mango enzyme (Srere et al. 1971). The PHMB‐treated enzyme also shows changes in its electrophoretic properties (Greenblatt and Sarkissian unpublished).The evidence presented here demonstrates that citrate synthase of various plants is sensitive to sulfhydryl reagents suggesting that sulfhydryl reactivity is a not unusual property of plant citrate synthase. In addition we show that molecular weight as large as or larger than that reported in microbial systems can occur in a blue‐green alga.