Kinetics of NO ligation with nitric-oxide synthase by flash photolysis and stopp

2019-06-18 01:01:42

NO NOS association oxide dissociation

责任者: Scheele, Jurgen S.;Bruner, Eric;Kharitonov, Vladimir G.;Martasek, Pavel;Roman, Linda J.;Masters, Bettie Sue Siler;Sharma, Vijay S.;Magde, Douglas 单位: Univ of California San Diego, La Jolla, CA, USA 来源出处: Journal of Biological Chemistry,1999,274(19):13105-13110 摘要: Nitric-oxide synthase (NOS) catalyzes conversion of L-arginine to nitric oxide, which subsequently stimulates a host of physiological processes. Prior work suggests that NOS is inhibited by NO, providing opportunities for autoregulation. This contribution reports that NO reacts rapidly (ka congruent 2×107 M-1 s-1) with neuronal NOS in both its ferric and ferrous oxidation states. Association kinetics are almost unaffected by L-arginine or the cofactor tetrahydrobiopterin. There is no evidence for the distinct two phases previously reported for association kinetics of CO. Small amounts of geminate recombination of NO trapped in a protein pocket can be observed over nanoseconds, and a much larger amount is inferred to take place at picosecond time scales. Dissociation rates are also very fast from the ferric form, in the neighborhood of 50 s-1, when measured by extrapolating association rates to the zero NO concentration limit. Scavenging experiments give dissociation rate constants more than an order of magnitude slower: still quite fast. For the ferrous species, extrapolation is not distinguishable from zero, while scavenging experiments give a dissociation rate constant near 10-4 s-1. Implications of these results for interactions near the heme binding site are discussed. 关键词: ;