Stimulation of human platelet guanylate cyclase by unsaturated fatty acid peroxides.

Abstract

Guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] activity of human platelet homogenates was stimulated by the addition of phospholipase A2 or unsaturated fatty acids such as oleic, vaccenic, linoleic, linolenic, eicosenoic, eicosadienoic and arachidonic acids. The addition of lipoxidase potentiated the fatty acid-induced stimulation of guanylate cyclase purified by DEAE-cellulose column chromatography. The extent of the stimulation was dependent on the concentration of the oxidized form of these fatty acids (peroxides). Saturated fatty acids such as stearic and arachidic acids had no effect on the guanylate cyclase activity in the presence or absence of lipoxidase, indicating that human platelet guanylate cyclase was stimulated by unsaturated fatty acid peroxides rather than by fatty acids. Hb prevented the enzyme stimulation produced by low concentrations of fatty acid peroxides, but enhanced stimulaton of the enzyme activity with high concentrations of fatty acid peroxides. 2-Mercaptoethanol, dithiothreitol, and N-ethylmaleimide inhibited the guanylate cyclase activities both in the presence and absence of unsaturated fatty acid peroxide. The stimulation of guanylate cyclase activity by unsaturated fatty acid peroxides was attributed to oxidation of sulfhydryl residues of the enzyme protein.