Effect of nitrite on microsomal cytochrome P-450.
1. Addition of nitrite to anaerobic rat liver microsomes leads to the appearance of a difference spectrum similar to the spectrum of the ferrous cytochrome P-450-NO complex. A Soret band is found at 444 nm in phenobarbital-stimulated microsomes but at 442 nm in 3-methylcholanthrene-stimulated microsomes. An alpha-band is located at 583 nm in both types of microsome. 2. The initial nitrite-induced difference spectrum is converted into a spectrum lacking a Soret band but with a prominent absorbance minimum at 417 nm. This is more rapid in microsomes from phenobarbital-treated animals where it is completed in 8 min than in microsomes from 3-methylcholanthrene-treated animals. A similar spectrum can be obtained by addition of nitrite to urea-treated microsomes in which cytochrome P-450 has been converted to cytochrome P-420. 3. Azo cleavage of neoprontosil in anaerobic microsomes is markedly inhibited by 1 mM nitrite. In contrast, oxidative drug metabolism is affected only by very high nitrite concentrations around 100 mM. It is concluded that in anaerobic microsomes, NO formed from nitrite complexes with ferrous cytochrome P-450 and thereby inhibits reductive drug metabolism.
D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D066298:In Vitro Techniques; D008027:Light; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009569:Nitric Oxide / Q000494:pharmacology; D009573:Nitrites / Q000494:pharmacology*; D051381:Rats; D013053:Spectrophotometry
D009573:Nitrites; D009569:Nitric Oxide; D003577:Cytochrome P-450 Enzyme System