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Related Experiment Videos

Novel substrates for nitric oxide synthases.

Ming Xian1, Noriko Fujiwara, Zhong Wen

  • 1Department of Chemistry, Wayne State University, Detroit, MI 48202, USA.

Bioorganic & Medicinal Chemistry
|July 12, 2002
PubMed
Summary
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Researchers explored how nitric oxide synthase (NOS) enzymes create nitric oxide (NO). They found that certain N-alkyl and N-aryl hydroxyguanidines act as novel substrates, offering insights into NOS enzyme activity and selectivity.

Area of Science:

  • Biochemistry
  • Enzymology
  • Medicinal Chemistry

Background:

  • Nitric oxide synthase (NOS) enzymes catalyze the production of nitric oxide (NO) through a two-step oxidation process.
  • The key intermediate in NO synthesis is N(G)-hydroxy-L-arginine (NOHA).
  • Understanding substrate specificity is crucial for probing enzyme mechanisms and developing targeted therapeutics.

Purpose of the Study:

  • To investigate the substrate specificity of the second enzymatic step in NOS activity.
  • To screen a series of N-alkyl and N-aryl substituted-N'-hydroxyguanidines as potential NOS substrates.
  • To identify novel substrates that can bypass the initial L-arginine to NOHA conversion step.

Main Methods:

  • Synthesis and evaluation of eleven N-alkyl-N'-hydroxyguanidines and five N-aryl-N'-hydroxyguanidines.

Related Experiment Videos

  • Enzymatic assays using the three major NOS isoenzymes: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS).
  • Determination of kinetic parameters (K(m)) for efficient substrates.

    • Main Results:

    • Several N-alkyl hydroxyguanidines (e.g., N-n-propyl, N-iso-propyl, N-n-butyl) were efficiently oxidized by all three NOS isoenzymes.
    • N-butyl-N'-hydroxyguanidine (4) showed optimal substrate activity for iNOS (K(m)=33 µM), and N-iso-propyl-N'-hydroxyguanidine (3) for nNOS (K(m)=56 µM).
    • N-aryl hydroxyguanidines, particularly N-phenyl-N'-hydroxyguanidine (K(m)=243 µM), were selective substrates for iNOS.

    Conclusions:

    • N-alkyl substituted hydroxyguanidines represent novel NOS substrates that 'short-circuit' the first oxidation step.
    • The size and nature of the alkyl substituent significantly influence substrate activity, suggesting steric and hydrophobic interactions within the NOS active site.
    • N-aryl hydroxyguanidines demonstrate isoform-selective substrate activity, offering potential for targeted modulation of NOS function.