DISSOCIATION OF NITRIC-OXIDE FROM SOLUBLE GUANYLATE-CYCLASE

Kinetic studies of soluble guanylate cyclase complexed with nitric oxi de prove that NO dissociation in the presence of the substrate GTP and Mg2+ is as much as 50 times faster than in their absence. In the pres ence of those two reagents the dissociation rate constant is k(obs) = 0.04 +/- 0.01 s(-1) at 20 degrees C, which is by far the fastest NO di ssociation rate constant ever reported for a ferrous heme protein. Ext rapolated to 37 degrees C, this corresponds to a half life of about 5 s for NO dissociation from soluble guanylate cyclase at physiological conditions, which is presumably fast enough to account for deactivatio n of the enzyme in biological systems. Dissociation rate constants are also reported for a variety of other reagent conditions. (C) 1997 Aca demic Press.