The broad objective of this proposal is to gain understanding of the mode of action of insulin. This goal is considered essential for the understanding of possible defects in diabetes mellitus and for the prevention of concomitants of the disease or of insulin therapy. The proposed research focuses on oxidative-reductive processes accompanying hormone action in rat fat cells. In particular the site of hydrogen peroxide production stimulated by insulin will be investigated. Attempts will be made to distinguish between the following candidates: membrane-bound NADPH oxidase, mitochondria and cytochrome P450. In addition, the hypothesis will be tested that intracellularly generated H2O2 has the capability of affecting glucose and lipid metabolism of fat cells.