Localization of Catalase A in Vacuoles ofSaccharomyces cerevisiae:Evidence for the Vacuolar Nature of Isolated "Yeast Peroxisomes"

The subcellular distribution of catalase A in the yeast Saccharomyces cerevisiae has been investigated. The enzyme was found to be bound to large particles, whereas most of the activity of catalase T was located in a 38 000 X g supernatant. Under various isolation conditions catalase A always showed a distribution among subcellular fractions virtually identical to that of two markers for vacuoles, proteinase B and alpha-mannosidase. More than 80 percent of the catalase A activity of a crude vacuole fraci-onercent of the catalase A activity of a crude vacuole fraction has been detected in purified vacuoles. Malate synthase, isocitrate lyase and glyoxylate reductase (NADP), three peroxisomal markers, showed a subcellular distribution significantly different from that of catalase A. It is concluded from these results that catalase A is specifically associated with the vacuoles of yeast. Like vacuoles, "peroxisomal" fractions isolated from yeast spheroplasts as described by Avers[1] contain only one catalase protein, catalase A. It could be shown by isopycnic and sedimentation velocity separations of crude mitochondrial fractions that catalase A in "peroxisomal" fractions is accompanied by considerable activities of proteinase B and alpha-mannosidase. From all our results it seems that the catalase-active particles isolated under such conditions are not typical peroxisomes but vesicles formed from vacuoles during the isolation procedure.