Studies on the membrane of Sarcina lutea

Abstract

Mild nonionic detergents were used to solubilize the pigment and two dehydrogenases from the membranes of S. lutea to study their properties. Previous studies on the membranes of S. lutea were largely on the function of the carotenoid pigments. It was alleged that the pigment is protein bound. No evidence could be found from gel filtration and electrophoretic experimentsfor association of the pigment with protein. Analyses showed that the solubilizedpigment was phospholipid associated. The pigment was functional in that it protected vitamin K in vitro from visible and near ultra-violet radiation. L-Malate and NADH dehydrogenases were completely solubilized from the membranes. Properties of the two enzymes in the membrane-bound and the solubilized state were studied. The activity of the bound Malate dehydrogenase was affected by modulators: (a) Cl ions, oxaloacetate, succinate and a-ketoglutarate caused inhibition to a small extent. (b) adenosine phosphates inhibited the activity strongly in the order ATP>ADP>AMP. (c) Nucleotides containing purine bases (NAD and NADP) in the oxidisedstate strongly inhibited and in the reduced state activated the enzyme activity. Most of these properties were retained by the solubilized enzyme. It was found that the enzyme required phospholipid for full activity. NADH dehydrogenase was found to be activated by NAD up to 10-5 M and inhibited above this concentration.A method of purification of the two dehydrogenases has been developed and a scheme for regulation of L-Malate metabolism has been proposed.