Analysis of the kinetics of CO binding to neuronal nitric oxide synthase by flash photolysis: Dual effects of substrates, inhibitors, and tetrahydrobiopterin

Simona Bengea, Yasuyuki Araki, Osamu Ito, Jotaro Igarashi, Ikuko Sagami, Toru Shimizu

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)

Abstract

The effects of substrates, inhibitors and tetrahydrobiopterin (H4B) on CO rebinding to the isolated heme-bound oxygenase domain (nNOSox) of neuronal nitric oxide synthase were examined by laser flash photolysis. The rate constant of CO recombination with substrate and inhibitor-free nNOSox in the absence of H4B was 1.0×106 M-1 s-1. The addition of H4B led to a marked decrease in the rate to 0.59×106 M -1 s-1. Interestingly, the substrates, L-Arg and N-hydroxy-L-Arg (NHA), altered CO binding behavior in that the binding rate was modified to CO concentration-independent, both with and without H4B. In the absence of H4B, agmatine, NG-monomethyl-L-Arg (NMMA) and N G-nitro-L-Arg methyl ester (NAME) decreased the CO concentration-dependent rate constants of rebinding by half (0.43×10 6 M-1 s-1 for the NMMA-bound complex), whereas N6-(l-iminoethyl)-L-Lys (NIL) and 7-nitro-1H-indazole (7-NI) increased the rate constants by more than 70% (up to 2.1×106 M-1 s-1 for the NIL-bound complex). In the presence of H4B, the binding rate was independent of CO concentration for the agmatine-bound complex. The differential effects of the inhibitors on the CO concentration-dependent rate constants were significantly diminished for the H4B-bound system. Interestingly, these variable effects of inhibitors on the CO binding rate were more pronounced in the absence of H4B. Accordingly, we suggest that H4B significantly influences CO binding by altering the CO access channel, and further reduces the divergent effects of different inhibitors.

Original languageEnglish
Pages (from-to)1210-1216
Number of pages7
JournalJournal of Inorganic Biochemistry
Volume98
Issue number7
DOIs
Publication statusPublished - 2004 Jul 1

Keywords

  • Arginine analogs
  • CO kinetics
  • Laser flash photolysis
  • Nitric oxide synthase
  • Tetrahydrobiopterin

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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