β Oxidation in Glyoxysomes from Castor Bean Endosperm

Abstract

Crude particulate preparations from castor bean endosperm contain most of the β oxidation activity present in initial extracts. Measurements on organelles separated by sucrose density centrifugation of the crude particles show that glyoxysomes (density 1.25) contain more than 80% of the particulate β oxidation activity, with virtually none in the mitochondria (density 1.19). Thiolase shows a similar distribution. Glyoxysomes do not oxidize NADH, but O2 is required for β oxidation. Addition of palmitoyl coenzyme A to glyoxysomes results in O2 uptake, NADH accumulation, and acetyl-CoA production, in a 0.5:1:1 stoichiometry. Cyanide has no effect on NADH accumulation, but doubles the rate of O2 uptake. These data are consistent with an O2-requiring oxidation of the prosthetic group of acyl-CoA dehydrogenase to yield H2O2, which is broken down by catalase in the glyoxysome. Acetyl-CoA produced by β oxidation is consumed in the glyoxylate cycle, which is also located in this organelle.