The tetrahydrobiopterin radical interacting with high- and low-spin heme in neuronal nitric oxide synthase - A new indicator of the extent of NOS coupling.

ABSTRACT: Reaction intermediates trapped during the single-turnover reaction of the neuronal ferrous nitric oxide synthase oxygenase domain (Fe(II)nNOS_OX) show four EPR spectra of free radicals. Fully-coupled nNOS_OX with cofactor (tetrahydrobiopterin, BH₄) and substrate (l-arginine) forms the typical BH₄ cation radical with an EPR spectrum ~4.0mT wide and hyperfine tensors similar to reports for a biopterin cation radical in inducible NOS_OX (iNOS_OX). With excess thiol, nNOSox lacking BH₄ and l-arg is known to produce superoxide. In contrast, we find that nNOS_OX with BH₄ but no l-arg forms two radicals with rather different, fast (~250μs at 5K) and slower (~500μs at 20K), electron spin relaxation rates

SUBMITTER: Krzyaniak MD 

PROVIDER: S-EPMC5362310 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature