Interactions between the isolated oxygenase and reductase domains of neuronal nitric-oxide synthase - Assessing the role of calmodulin

E A Rozhkova, N Fujimoto, I Sagami, S N Daff, T Shimizu, Simon Daff

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Abstract

Nitric-oxide synthase (NOS) is a fusion protein composed of an oxygenase domain with a heme-active site and a reductase domain with an NADPH binding site and requires Ca2+/calmodulin (CaM) for NO formation activity. We studied NO formation activity in reconstituted systems consisting of the isolated oxygenase and reductase domains of neuronal NOS with and without the CaM binding site. Reductase domains with 33-amino acid C-terminal truncations were also examined. These were shown to have faster cytochrome c reduction rates in the absence of CaM. N-G-hydroxy-L-Arg, an intermediate in the physiological NO synthesis reaction, was found to be a viable substrate. Turnover rates for N-G-hydroxy-L-Arg in the absence of Ca2+/CaM in most of the reconstituted systems were 2.3-3.1 min(-1). Surprisingly, the NO formation activities with CaM binding sites on either reductase or oxygenase domains were decreased dramatically on addition of Ca2+/CaM. However, NADPH oxidation and cytochrome c reduction rates were increased by the same procedure. Activation of the reductase domains by CaM addition or by C-terminal deletion failed to increase the rate of NO synthesis. Therefore, both mechanisms appear to be less important than the domain-domain interaction, which is controlled by CaM binding in wild-type neuronal NOS, but not in the reconstituted systems.

Original languageEnglish
Pages (from-to)16888-16894
Number of pages7
JournalJournal of Biological Chemistry
Volume277
Issue number19
DOIs
Publication statusPublished - 10 May 2002

Keywords

  • ELECTRON FLOW-THROUGH
  • CONTROL ELEMENT
  • FLAVIN
  • SITE
  • ACTIVATION
  • EXPRESSION
  • BINDING
  • RECONSTITUTION
  • IDENTIFICATION
  • CATALYSIS

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