| Autor: |
Scheele, J S, Bruner, E, Kharitonov, V G, Martásek, P, Roman, L J, Masters, B S, Sharma, V S, Magde, D |
| Zdroj: |
Journal of Biological Chemistry; May 1999, Vol. 274 Issue: 19 p13105-10, 6p |
| Abstrakt: |
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 with 2 x 10(7) 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. |
| Databáze: |
Supplemental Index |
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