Journal of Biological Chemistry

EC 2.7.1.1) activity was determined in subcellular fractions prepared from pea (Pisurn satiuurn) leaf ho-mogenates. About 60 % of the total detectable activity of hexokinase was found associated with a particulate fraction consisting essentially of mitochondria and chloroplasts and free of cytosol contamination. The hexokinase specific activity of the particulate fraction was 2-fold higher than that of the homogenate and about 4-fold higher than that of the cytosol. Using a specially designed isokinetic-isopycnic su-crase density gradient centrifugation method, the dis-tribution of hexokinase activity correlated with that of the mitochondrial marker (cytochrome oxidase) and not with that of the chloroplast membrane marker (chlorophyll) or that of the cytosol marker (phosphoen-