Description (applicant's description): Organizing principles in cell biology are emerging now that help elucidate many earlier reports of links between lipoxygenases and disease states. Because oxidation products of unsaturated lipids (lipoxygenase products and others) are short-lived signaling molecules that act locally (autocrine and paracrine mediators), experiments with isolated components (the enzymes and molecules with which they interact) are used to determine mechanisms of action. The experiments proposed focus on species with unpaired electrons related to lipoxygenase mechanisms and address how electrons redistribute in catalytic intermediates. EPR spectroscopy is the primary biophysical tool to be applied in these studies. High frequency EPR, at 94 GHz, will be employed in many experiments. Specific aims: 1) The electronic structure of nitric oxide in the complex with iron in lipoxygenase will be determined by EPR. The complex is a model of iron-ligand interactions in lipoxygenase. Methods include high frequency EPR of frozen solutions and crystals and, in collaboration, lower frequency pulsed EPR. (2) The roles of two different tyrosines in a protein with activity downstream of lipoxygenase action (allene oxide synthase) will be determined. (3) The electronic structure of different oxidation states of a manganese-containing lipoxygenase will be examined by high frequency EPR.