title: Further characterization and purification of the flavin-dependent S-benzyl-L-cysteine S-oxidase activities of rat liver and kidney microsomes.
abstract: Previously, we provided evidence that cysteine conjugate S-oxidase (S-oxidase) activities of rat liver and kidney microsomes may be associated with flavin-containing monooxygenases (FMOs). In this study, the biochemical properties of these activities were further investigated. When NADPH was replaced by NADH, the S-oxidase activities were reduced significantly. Removal of the flavin moiety from microsomes significantly reduced the S-oxidase activities; however, addition of exogenous FAD or FMN restored the activities of the flavin-depleted microsomes. Solubilization of hepatic or renal microsomes with Emulgen 911, Nonidet P-40, Triton X-100, or 3-[(3-cholamidopropyl)dimethyl-ammonio]-1- propane sulfate or inclusion of the sulfhydryl-reactive agents Hg2+, N-ethylmaleimide, or iodoacetamide did not affect the S-oxidase activities, whereas solubilization of either hepatic or renal microsomes by cholate or heating of renal microsomes in the absence of NADPH significantly reduced the S-oxidase activities. In addition to male rat hepatic and renal microsomes, the S-oxidase activities were detected in lung microsomes of male rats and hepatic and renal microsomes of male mice and female rats and rabbits. The male rat kidney maintained the highest S-oxidase activity of all species and tissues examined. Whereas the aforementioned results provided further evidence for the S-oxidase activities being associated with FMOs, unambiguous evidence for this hypothesis was provided by the purification of the activities from rat liver (580-fold) and kidney (700-fold) microsomes and by the use of the isolated proteins in polyacrylamide gel electrophoresis, flavin content determinations, amino-terminal amino acid sequence analysis, amino acid composition analysis, and substrate kinetic studies. The findings that the S-oxidases were immunoreactive with antibodies raised against the pig liver 1A1 isozyme but not with antibodies raised against the rabbit lung 1B1 isozyme and that the liver S-oxidase amino-terminal amino acid sequence was more comparable to the amino-terminal amino acid sequences of pig and rabbit liver 1A1 isozymes than to those of rabbit lung 1B1 and liver 1D1 isozymes provide evidence that the S-oxidases are related to the known FMO 1A1 isozymes.
authors.affiliation: Department of Comparative Biosciences, University of Wisconsin, Madison 53706.
authors.forename: P J
authors.initials: PJ
authors.lastname: Sausen
authors.forename: R J
authors.initials: RJ
authors.lastname: Duescher
authors.forename: A A
authors.initials: AA
authors.lastname: Elfarra
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D015153:Blotting, Western; D003902:Detergents; D005260:Female; D005486:Flavin Mononucleotide / Q000032:analysis / Q000378:metabolism; D005182:Flavin-Adenine Dinucleotide / Q000032:analysis; D006358:Hot Temperature; D007527:Isoenzymes; D007668:Kidney / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D000227:Adenine Nucleotides; D000596:Amino Acids; D003902:Detergents; D007527:Isoenzymes; D013439:Sulfhydryl Reagents; D005182:Flavin-Adenine Dinucleotide; D005486:Flavin Mononucleotide; D010088:Oxidoreductases; C063574:cysteine conjugate S-oxidase