Surface Charge of Biological Membranes as a Possible Regulator of Membrane‐Bound Enzymes

Abstract

Glycerol‐3‐phosphate dehydrogenase of insect thoracic muscle mitochondria and arylsulphatase C of rat liver microsomes were inhibited by anionic surface‐active agents oleate, palmitoyl‐CoA and sodium dodecylsulphate, and activated by cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride. Dimethylaniline oxidase of rat liver microsomes were inhibited by cationic surfactants and activated by anionic surfactants. The inhibition of NADH dehydrogenase of rat liver submitochondrial particles by NAD+ was potentiated by the anionic surfactants and partly released by cetyltrimethylammonium bromide. These surface‐active activators and inhibitors altered apparent Km values of the enzymes but did not change the activities at infinite substrate concentration (V values). This effect of surfactants disappeared after solubilization of the membranes and re‐appeared after incorporating the solubilized enzyme into phospholipid vesicles. Cationic surfactants decreased whereas anionic surfactants increased the negative surface charge and surface potential of mitochondria, submitochondrial particles and microsomes, as measured by free electrophoresis of the particles and binding of 8‐anilino‐1‐naphthalene sulphonate. Calculations based on Km change and the change of surface potential agree well with the assumption that a change of the surface charge density alters local concentrations of the substrates and/or the products in the vicinity of the membrane. Possible role of factors affecting the surface charge of biological membranes in controlling the activity of membrane‐bound enzymes is discussed.