THE DEACTIVATION OF SOLUBLE GUANYLYL CYCLASE BY REDOX-ACTIVE AGENTS

Soluble guanylyl cyclase (sGC), an enzyme involved in cGMP signal tran sduction, is activated by NO binding to the endogenous heme. The mecha nism of deactivation is not known. In tissues, cGMP levels decrease wi thin minutes, despite the fact that sGC is activated to levels above t he phosphodiesterase activity, Simple dissociation of NO from the heme in sGC has been suggested as a possible deactivation mechanism; howev er, dissociation rates of NO from ferrous heme proteins are typically very slow. Since oxidants and reductants are known to affect sGC activ ity, we have tested the effect of a variety of redox-active agents on the activity of NO-activated sGC. All the redox-active compounds teste d, covering a wide range of reduction potentials, selectively deactiva ted the NO-activated sGC while having little or no effect on the basal activity of the enzyme, Among the reagents studied in detail, deactiv ation of sGC by air occurred slowly, while deactivation by ferricyanid e was faster and methylene blue was fastest. The mechanism of deactiva tion of sGC by dioxygen in the air is straightforward: the heme is oxi dized to Fe(III)heme and nitrate is formed. This reaction is similar t o that of dioxygen with NOHb and NOMb as occurs in cured meats. Methyl ene blue and ferricyanide deactivate sGC by a different, as yet undete rmined, mechanism. (C) 1998 Academic Press.