Membranes of glyoxysomes from castor-bean endosperm. Enzymes bound to purified-membrane preparations.

Abstract

A procedure was developed for the isolation of membranes of glyoxysomes from the endosperm of germinating castor beans (Ricinus communis L. var. zanzibariensis). These membranes were prepared by osmotic‐shock treatment of isolated glyoxysomes. In some cases this was followed by mild sonication. They were isolated by centrifugation on to a 57% (w/w) sucrose layer and purified by isopycnic sucrose gradient centrifugation.The membrane preparations were characterized by electronmicroscopy and assayed for enzyme activities. They consisted mainly of ghost‐type vesicles and were found to contain a major part of fatty acid β‐oxidation, malate synthase, citrate synthase and antimycin‐A‐insensitive NADH‐cytochrome c reductase activities of the whole glyoxysomes. Malate dehydrogenase may also be bound to the membrane to a significant extent. A tentative scheme is postulated describing the structural organization of fatty acid β‐oxidation and of the glyoxylate cycle in glyoxysomes.