title: Guanethidine N-oxide formation as a measure of cellular flavin-containing monooxygenase activity.
abstract: The usefulness of guanethidine N-oxide formation as a measure of cellular flavin-containing monooxygenase activity was assessed using the purified hog liver enzyme, rat liver microsomes and hepatocytes. The apparent Km and Vmax for this reaction in hepatocytes were 0.30 +/- 0.20 mM and 0.81 +/- 0.36 nmole per 10(6) cells min-1 respectively. The Km for the purified enzyme was 0.31 mM and the Vmax was 0.56 nmole per microgram enzyme min-1. 2-Diethylaminoethyl-2,2-diphenyl valerate (SKF-525A) at a concentration of 0.5 mM had no effect on guanethidine N-oxide formation by either rat liver microsomes or the purified enzyme. In contrast 2,4-dichloro-6-phenylphenoxyethylamine (DPEA) at the same concentration caused greater than a 100% increase in the microsomal production of guanethidine N-oxide. The tertiary amines imipramine, chloropromazine and methylpyrilene inhibited N-oxide formation by both hepatocytes and the purified enzyme. These data indicate that guanethidine N-oxide formation can be used as a measure of cellular flavin-containing monooxygenase activity.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D008099:Liver / Q000201:enzymology; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000201:enzymology; D010105:Oxygenases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013552:Swine
chemical_list: D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming)