A kinetic model of the system: tyrosyl radical-nitrogen oxide-superoxide ion

It is generally recognized that the initial step in the formation of atherosclerotic plaque in humans involves the peroxidation of low density lipoproteins (LDL). However, there is no agreement on the mechanism that initiates peroxidation. Among the candidates are several that involve tyrosyl radical, nitrogen oxide, and superoxide ion or their mutual reaction products. In this paper a kinetic model of this system is constructed that examines the nature of these reactions, and places some constraints on their possible overall contribution to the initiation of peroxidation. The reversible reaction of nitric oxide and tyrosyl radical acts to "buffer" tyrosyl radical concentrations while the reaction of tyrosyl radical with superoxide ion scavenges tyrosyl radical. Quantitatively, the reaction of nitric oxide with superoxide to form peroxynitrite is a more important process, but the physiological significance would appear to be related to details of the decay of peroxynitrite that are still in dispute.