Functional changes of rat brain mitochondrial enzymes induced by monomeric cholesterol

The binding of [14C]cholesterol into rat brain mitochondrial membranes follows an exponential path described by the general formula y = a X ebx. [14C]cholesterol glucoside binding has a sigmoidal character where the "best-fit" curve of this type of binding is the one described by the Hill equation with Hill coefficient h = 2.06. These findings suggest a positive cooperativity in the binding of both compounds into rat brain mitochondrial membranes. The specific activity of the outer mitochondrial membrane enzyme monoamine oxidase was linearly decreased at different concentration of cholesterol or its glucoside. The specific activity of the inner mitochondrial membrane enzyme succinate-cytochrome c reductase was linearly decreased, while that of Rotenone-sensitive NADH-cytochrome c reductase was exponentially increased, at different concentrations of cholesterol. These results are discussed in terms of specific interactions of cholesterol with constituent mitochondrial membrane lipids and their implications for deviations from normal neuronal function.