title: Microsomal N-depropargylation of pargyline to propiolaldehyde, an irreversible inhibitor of mitochondrial aldehyde dehydrogenase.
abstract: Rat liver microsomes catalyzed the conversion of pargyline (N-methyl-N-propargylbenzylamine) to propiolaldehyde, a potent inhibitor of the low Km mitochondrial aldehyde dehydrogenase (AlDH) isozyme. The involvement of cytochrome P-450 in vivo was shown indirectly by (a) the ability of SKF-525A to block pargyline-induced acetaldehydemia, (b) the prolongation of phenobarbital sleeping time by pargyline, and (c) the enhancement of pargyline-induced acetaldehydemia by phenobarbital pretreatment. Propiolaldehyde was isolated as its semicarbazone by incubating pargyline with either phenobarbital-induced or uninduced rat liver microsomes and an NADPH-generating system, the latter being required for propiolaldehyde formation. In vitro studies with liver mitochondria showed that propiolaldehyde inhibition of AlDH was temperature- and time-dependent and irreversible. We propose that the cytochrome P-450 catalyzed conversion of pargyline to its active metabolite, propiolaldehyde, proceeds via a mechanism involving N-depropargylation, viz., hydroxylation of pargyline alpha to the acetylenic bond forming a carbinolamine intermediate, followed by dissociation.
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000037:antagonists & inhibitors*; D000447:Aldehydes / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000201:enzymology*; D010293:Pargyline / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology; D011335:Proadifen / Q000494:pharmacology; D051381:Rats
chemical_list: D000447:Aldehydes; D007527:Isoenzymes; C018132:propiolaldehyde; D003577:Cytochrome P-450 Enzyme System; D010293:Pargyline; D011335:Proadifen; D000445:Aldehyde Oxidoreductases; D010634:Phenobarbital