Isoenzymes of Pyruvate Kinase in Etioplasts and Chloroplasts

Abstract

Isoenzymes of pyruvate kinase from green leaves of castor [Ricinus communis cv. Baker] bean and etiolated leaves of pea [Pisium sativum cv. Little Marvel] plants have been separated by ion filtration chromatography. One of the isoenzymes is localized in the plastid, whereas the other is in the cytosol. The cytosolic enzyme has a pH optimum from pH 7-pH 9, and utilizes nucleotides other than ADP as the phosphoryl acceptor. The plastid enzyme has a much sharper optimum at pH 8, and is less efficient at using alternative nucleotides. The plastic pyruvate kinase, unlike the cytosolic enzyme, requires the presence of dithiothreitol or 2-mercaptoethanol during isolation and storage to stabilize the activity.