Interactions of Mitochondrial Matrix Enzymes with Mitochondrial Inner Membranes

Abstract

We have shown previously that citrate synthase (EC 4.1.3.7), mitochondrial malate dehydrogenase (EC 1.1.1.37), and fumarase (EC 4.2.1.2) bind to the matrix surface of the inner mitochondrial membrane (D’Souza and Srere, 1983). These experiments, along with others, were taken as evidence to support a hypothesis which proposes that there is an organization of Krebs TCA cycle enzymes with their metabolically sequential neighbors and with protein components of the inner membrane (Srere, 1985). The three enzymes studied were selected because of their availability and their stability. Since succinate dehydrogenase (EC 1.3.99.1) and α-ketoglutarate dehydrogenase complex (EC 2.3.1.61, 1.6.4.3, 1.2.4.1) are already known to be tightly bound to the inner membrane, the only remaining Krebs TCA cycle enzymes to be studied were aconitase, (NAD⁺) isocitrate dehydrogenase (EC 1.1.1.41) and succinyl CoA synthetase (EC 6.2.1.4). An inner-membrane associated (NAD⁺)isocitrate dehydrogenase has been isolated from potato mitochondria (Teszuka and Laties, 1983). We have also shown that certain mitochondrial dehydrogenases (malate,α-ketoglutarate, pyruvate and β-hydroxyacyl CoA) bind to Complex I, an inner membrane protein (Sumegi and Srere, 1984). We could not detect the binding of (NAD⁺)isocitrate dehydrogenase to Complex I.