Isoenzymes of Pyruvate Kinase in Etioplasts and Chloroplasts

Isoenzymes of pyruvate kinase from green leaves of castor bean and etiolated leaves of pea 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 to pH 9, and is able to utilize 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.