Membranes of rat liver peroxisomes

Properties of a transplasma membrane redox system of Phanerochaete chrysosporium

A transplasma membrane redox system of Phanerochaete chrysosporium was studied using ferricyanide, a membrane-impermeable electron acceptor. Rates of reduction were dependent upon initial ferricyanide concentration and mycelial mass. Specific activities of 12 +/- 2 nmol/min/mg mycelia (dry wt) were consistently obtained using nutrient-sufficient mycelia at pH 8.0 and 10 mM ferricyanide. Upon nutrient limitation (either carbon or nitrogen), activity decreased. Reduction was inhibited by carbonyl cyanide m-chloromethoxyphenyl hydrazone, 2,4-dinitrophenol, and sodium azide but not by potassium cyanide at 100 nmol/mg mycelia. Ferricyanide reduction and proton export rates increased with pH above the physiological pH for the fungus. The stimulation in proton exported by the addition of ferricyanide was equal to the rate of ferricyanide reduced at pH 8.0 when Hepes buffer was used. The relevance of these findings with regard to the physiological pH optimum of the fungus and the metabolism of pollutants by this fungus is discussed.

Electron transport in purified glyoxysomal membranes from castor-bean endosperm

Glyoxysomes isolated from castor-bean (Ricinus communis L.) endosperm were treated with water, 0.2 M KCl, 1 M KCl, or 0.1 M Na2CO3. Glyoxysomal sacs, i.e. membranes which retained some visible matrix, resulted from the treatments with water and KCl. Glyoxysomal ghosts, i.e. intact membranes free of matrix, were only obtained following treatment with carbonate. The ghosts were free of activities of matrix enzymes, particularly palmitoyl-CoA oxidation, isocitrate dehydrogenase (EC 1.1.1.42) and isocitrate lyase (EC 4.1.3.1), and contained only negligible amounts of malate synthase (EC 4.1.3.2), malate dehydrogenase (EC 1.1.1.37), β-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.98) and catalase (EC 1.11.1.6). Distribution and appearance of membrane-associated particles in the protoplasmic and ectoplasmic faces of freeze-fracture replicas of the glyoxysomal membrane were the same in intact tissue, isolated glyoxysomes, and ghosts. Membranes purified by treatment with 0.2 M KCl or 0.1 M carbonate catalyzed the reduction of cytochrome-c when NADH or NADPH was provided as the electron donor. β-Oxidation, localized in the matrix, could be linked to reduction of cytochrome-c or ferricyanide when purified membranes were combined with the matrix supernatant. Cytochrome-c could also be reduced by coupling enzyme activities in the matrix, NADP-isocitrate dehydrogenase or malate dehydrogenase, with those of the membrane. These results indicate that electrons from β-oxidation, malate oxidation or isocitrate oxidation can be transferred directly to the redox components of the glyoxysomal membrane. We, therefore, conclude that any NADH and NADPH formed by enzymes in the matrix can be recycled continuously within the organelle.