Efforts in this laboratory will be directed toward projects on spinach nitrate reductase and adrenal mitochondrial and microsomal hydroxylation systems. I. Nitrite Reductase. In the coming year, much effort will be devoted to purifying large quantities of enzyme by methods already established in this laboratory. We will then do stopped-flow studies, chemical studies of the siroheme group, and an extension of EPR studies. II. Adrenal Hydroxylating Systems. In the adrenal mitochondrial systems, we will extend our efforts at isolating adrenal cytochrome P-450 and in establishing the mechanism of its interaction with the flavoprotein and iron-sulfur protein of the hydroxylating system, as well as its interactions with substrate, oxygen, and CO. We will also initiate studies on the nature and biological role of the adrenal microsomal hydroxylating system.