Basis of Guanylate Cyclase Activation by Carbon Monoxide

• Published in: Proceedings of the National Academy of Sciences - PNAS 1995-03, Vol.92 (7), p.2568-2571
• Main Authors: Kharitonov, Vladimir G., Sharma, Vijay S., Pilz, Renate B., Magde, Douglas, Koesling, Doris
• Format: Article
• Language: English
• Subjects: Absorption spectra; Animals; Binding Sites; Biochemistry; Carbon monoxide; Carbon Monoxide - pharmacology; Catalysts; Cattle; Enzyme Activation; Enzymes; Guanylate Cyclase - chemistry; Guanylate Cyclase - metabolism; Heme - chemistry; Heme - metabolism; Hemeproteins; Hemoglobins; Humans; Kinetics; Lasers; Ligands; Lung - enzymology; Nitrosyls; Proteins; Serum Albumin - chemistry; Serum Albumin - metabolism; Spectrophotometry; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.7.2568

Kinetics of CO association with guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2] and dissociation from carboxy guanylate cyclase have been studied at pH 7.5 by flash photolysis, yielding rate constants at 23/circC of 1.2 ± 0.1 x 105M-1.sec-1and 28 ± 2 sec-1, respectively. While the CO combination rate constant is the same as for the T state of hemoglobin, the CO dissociation rate constant is much higher than expected for a six-coordinate carboxyheme protein; yet the absorption spectrum is indicative of a six-coordinate heme. The two observations are reconciled by a reaction mechanism in which CO dissociation proceeds via a five-coordinate intermediate. This intermediate is structurally very similar to the five-coordinate nitrosyl heme derivative of guanylate cyclase and is presumably responsible for the observed 4-fold activation of guanylate cyclase by CO. Thus, we provide a model that explains enzyme activities of the nitrosyl and carboxy forms of the enzyme on the basis of a common mechanism.