Revisiting the kinetics of nitric oxide (NO) binding to soluble guanylate cyclase: the simple NO-binding model is incorrect

Proc Natl Acad Sci U S A. 2002 Sep 17;99(19):12097-101. doi: 10.1073/pnas.192209799. Epub 2002 Sep 3.


Soluble guanylate cyclase (sGC) is a ferrous iron hemoprotein receptor for nitric oxide (NO). NO binding to the heme activates the enzyme 300-fold. sGC as isolated is five-coordinate, ferrous with histidine as the axial ligand. The NO-activated enzyme is a five-coordinate nitrosyl complex where the axial histidine bond is broken. Past studies using rapid-reaction kinetics demonstrated that both the formation of a six-coordinate intermediate and the conversion of the intermediate to the activated five-coordinate nitrosyl complex depended on the concentration of NO. A model invoking a second NO molecule as a catalyst for the conversion of the six-coordinate intermediate to the five-coordinate sGC-NO complex was proposed to explain the observed kinetic data. A recent study [Bellamy, T. C., Wood, J. & Garthwaite, J. (2002) Proc. Natl. Acad. Sci. USA 99, 507-510] concluded that a simple two-step binding model explains the results. Here we show through further analysis and simulations of previous data that the simple two-step binding model cannot be used to describe our results. Instead we show that a slightly more complex two-step binding model, where NO is used as a ligand in the first step and a catalyst in the second step, can describe our results quite satisfactorily. These new simulations combined with the previous activation data lead to the conclusion that the intermediate six-coordinate sGC-NO complex has substantial activity. The model derived from our simulations also can account for the slow deactivation of sGC that has been observed in vitro.

Publication types

  • Comparative Study

MeSH terms

  • Alcaligenes / metabolism
  • Computer Simulation
  • Cytochrome c Group / metabolism
  • Enzyme Activation
  • Guanylate Cyclase / metabolism*
  • In Vitro Techniques
  • Kinetics
  • Models, Biological*
  • Nitric Oxide / metabolism*
  • Signal Transduction
  • Solubility
  • Spectrophotometry


  • Cytochrome c Group
  • Nitric Oxide
  • Guanylate Cyclase