Polypeptide and phospholipid composition of the membrane of rat liver peroxisomes: comparison with endoplasmic reticulum and mitochondrial membranes.

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Abstract
Membranes were isolated from highly purified peroxisomes, mitochondria and rough and smooth microsomes of rat liver by the 1-step Na2CO3 procedure described previously. The polypeptide compositions of these membranes determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis were greatly dissimilar. The peroxisomal membrane contains 12% of the peroxisomal protein and consists of 3 major polypeptides (21,700, 67,700 and 69,700 daltons) as well as some minor polypeptides. The major peroxisomal membrane proteins as well as most of the minor ones are absent from the endoplasmic reticulum (ER). Most ER proteins are absent from peroxisomes. By EM, purified peroxisomal membranes are .apprx. 6.8 nm thick and have a typical trilaminar appearance. The phospholipid/protein ratio of peroxisomal membranes is .apprx. 200 nmol/mg; the principal phospholipids are phosphatidyl choline and phosphatidyl ethanolamine, as in ER and mitochondrial membranes. In contrast to the mitochondria, peroxisomal membranes contain no cardiolipin. All the membranes investigated contain a polypeptide band with a molecular mass of .apprx. 15,000 daltons. Whether this represents an exceptional common membrane protein or a coincidence is unknown. The implications of these results for the biogenesis of peroxisomes are discussed.