Autoxidation rates of neuronal nitric oxide synthase: Effects of the substrates, inhibitors, and modulators

H Sato, I Sagami, S Daff, T Shimizu

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Abstract

Autoxidation rates of the full-length neuronal nitric oxide synthase (nNOS) were analyzed and found to be composed of three phases, 60 s(-1) (28%), 5.5 s(-1) (11%) and 0.048 s(-1) (61%), Addition of L-Arg, N-G-hydroxy-L-Arg (NHA), and N-G-monomethyl-L-Arg markedly decreased the rate constants for the first and second phases down to 12-20 s(-1) and 0.32-2.6 s(-1), respectively. Addition of (6R)-5,6,7,8-tetrahydro-L-biopterin (H4B) increased the amplitude of the second phase up to 29% of the total. Addition of NHA decreased the rate of the first phase by 4.4-fold in the presence of H4B, whereas addition of L-Arg and other modulators did not significantly affect the rates under the same conditions. Thus, we deduce that (1) L-Arg stabilizes the O-2-bound ferrous complex for efficient O-O bond cleavage to occur; (2) H4B influences the O-2-bound ferrous complex in a fashion different from L-Arg; and (3) NHA induces a characteristic distal-site structure in the presence of H4B, reflecting a difference in the mechanism of activation of O-2 in the first step (monooxygenation of L-Arg) and the second step (monooxygenation of NHA). (C) 1998 Academic Press.

Original languageEnglish
Pages (from-to)845-849
Number of pages5
JournalBiochemical and Biophysical Research Communications
Volume253
Issue number3
Publication statusPublished - 30 Dec 1998

Keywords

  • oxidation
  • nitric oxide synthase
  • cytochrome P450
  • hemoprotein
  • stopped flow
  • HYDROXY-L-ARGININE
  • CATALYTIC FUNCTION
  • CYTOCHROME-P450D
  • CONVERSION
  • CITRULLINE
  • MECHANISM
  • REDUCTASE
  • SITE

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