Localization of Enzymes of Glycolate Metabolism in the Alga Chlorogonium elongatum.
Organelles in homogenates from autotrophic cells of Chlorogonium elongatum were separated on linear sucrose gradients. The distribution of enzymes typical of leaf peroxisomes was determined.Whereas more than 60% of the catalase activity was particulate and recovered in microbodies at a mean density of 1.225 g/cm(3) within the gradient, in most experiments only 5 to 10% (as a maximum 30%) of the NAD-dependent hydroxypyruvate reductase was particulate, and this was recovered principally at density 1.19 g/cm(3). This distribution coincides with that of cytochrome oxidase, malate dehydrogenase, and isocitrate dehydrogenase, the mitochondrial markers. Glyoxylate-glutamate aminotransferase and glycolate dehydrogenase showed a similar distribution pattern to that of NAD-dependent hydroxypyruvate reductase. Thus in Chlorogonium the enzymes of the glycolate pathway are not associated with the microbodies that are recovered at density 1.225 g/cm(3).The single large chloroplasts of the Chlorogonium cells are broken during grinding, and this probably accounts for the finding that NADP-glyoxylate reductase was recovered only in the soluble fractions of the gradient.
Stabenau
H
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Division of Natural Sciences, University of California, Santa Cruz, California 95064.