SYNERGISTIC ACTIVATION OF SOLUBLE GUANYLATE-CYCLASE BY YC-1 AND CARBON-MONOXIDE - IMPLICATIONS FOR THE ROLE OF CLEAVAGE OF THE IRON-HISTIDINE BOND DURING ACTIVATION BY NITRIC-OXIDE
Jr. Stone et Ma. Marletta, SYNERGISTIC ACTIVATION OF SOLUBLE GUANYLATE-CYCLASE BY YC-1 AND CARBON-MONOXIDE - IMPLICATIONS FOR THE ROLE OF CLEAVAGE OF THE IRON-HISTIDINE BOND DURING ACTIVATION BY NITRIC-OXIDE, Chemistry & biology, 5(5), 1998, pp. 255-261
Background: Nitric oxide (. NO) is used in biology as both an intercel
lular signaling agent and a cytotoxic agent. In signaling, submicromol
ar quantities of . NO stimulate the soluble isoform of guanylate cycla
se (sGC) in the receptor cell. . NO increases the V-max of this hetero
dimeric hemoprotein up to 400-fold by interacting with the heme moiety
of sGC to form a 5-coordinate complex. Carbon monoxide (CO) binds to
the heme to form a 6-coordinate complex, but only activates the enzyme
5-fold. YC-1 is a recently discovered compound that relaxes vascular
smooth muscle by stimulating sGC, Results: In the presence of YC-1, CO
activates sGC to the same specific activity as attained with . NO. YC
-1 did not affect the NO-stimulated activity. The on-rate (k(on)) and
off-rate (k(off)) of CO for binding to sGC in the presence of YC-1 wer
e determined by stopped-flow spectrophotometry. Neither the k(on) nor
the k(off) varied from values previously obtained in the absence of YC
-1, indicating that YC-1 has no effect on the affinity of CO for the h
eme, In the presence of YC-1, the visible spectrum of the sGC-CO compl
ex has a Soret peak at 423 nm, indicating the complex is 6-coordinate.
Conclusions: YC-1 has no effect on the affinity of CO for the heme of
sGC. In the presence of YC-1, maximal activation of sGC by CO is achi
eved by formation of a 6-coordinate complex between CO and the heme in
dicating that cleavage of the Fe-His bond is not required for maximal
activation of sGC.