Protein phosphorylation in peroxisomes

The possible presence of phosphorylated proteins in peroxisomes was studied in hepatocytes from nafenopin-treated and normal rats. A 63 kDa phosphorylated protein was consistently and exclusively found in the membrane of peroxisomes from hepatocytes incubated in the presence of ³²P-phosphate. The peroxisomes were isolated in metrizamide isopycnic gradients of postnuclear supernatants and were subfractionated by alkaline extraction to separate the membrane and the matrix proteins. Polyacrylamide gel electrophoresis, autoradiography and densitometry were employed to characterize the proteins. The 63 kDa membrane protein copurifies with peroxisomes in metrizamide gradients and apparently can be phosphorylated, in purified peroxisomes, with ATP and catalytic subunit of cAMP-dependent protein kinase.