title: Mechanism of delta-aminolevulinate dehydratase inhibition by phenyl selenoacetylene involves its conversion to diphenyl diselenide.
abstract: The mechanism of delta-aminolevulinate dehydratase (delta-ALA-D) inhibition by phenyl selenoacetylene in vitro was investigated in this study. Phenyl selenoacetylene (40-400 microM) inhibition of delta-aminolevulinate dehydratase from rat liver (low speed supernatant fraction, S1 fraction) was partially prevented by incubation under argon atmosphere and completely prevented by dithiothreitol. After incubation with S1 fraction from rat liver or cysteine (40 mM), phenyl selenoacetylene was partially converted into diphenyl diselenide, which is a stronger inhibitor of delta-aminolevulinate dehydratase than phenyl selenoacetylene. Diphenyl diselenide increased the rate of oxidation of -SH groups, while phenyl selenoacetylene did not affect such oxidation. delta-Aminolevulinate dehydratase purified from bovine liver (Sigma) was less sensitive to phenyl selenoacetylene and diphenyl diselenide than the enzyme from S1 fraction. We propose that the lower sensitivity of purified enzyme to selenides could be related to the formation of selenols due to the presence of dithiothreitol (a reducing agent) in the incubation medium. In agreement, incubation of purified enzyme (Sigma) with diphenyl diselenide (2 microM) and sodium borohydride (a reducing agent) under argon atmosphere significantly increased enzyme activity. Results obtained suggest that delta-aminolevulinate dehydratase inhibition by phenyl selenoacetylene is dependent on its conversion into diphenyl diselenide that induces oxidation of essential -SH groups of delta-aminolevulinate dehydratase. We propose that oxygen could be important in the regeneration of diphenyl diselenide leading to a catalytic oxidation of the enzyme.
authors.affiliation: Departamento de Química, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
authors.forename: Vanderlei
authors.initials: V
authors.lastname: Folmer
authors.forename: Rodrigo Cordeiro
authors.initials: RC
authors.lastname: Bolzan
authors.forename: Marcelo
authors.initials: M
authors.lastname: Farina
authors.forename: Gilson
authors.initials: G
authors.lastname: Zeni
authors.forename: Cristina Wayne
authors.initials: CW
authors.lastname: Nogueira
authors.forename: Tatiana
authors.initials: T
authors.lastname: Emanuelli
authors.forename: João Batista Teixeira
authors.initials: JB
authors.lastname: Rocha
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D001555:Benzene Derivatives / Q000493:pharmacokinetics / Q000494:pharmacology*; D001711:Biotransformation; D001894:Borohydrides / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D016566:Organoselenium Compounds / Q000493:pharmacokinetics / Q000494:pharmacology*; D010084:Oxidation-Reduction; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors*; D051381:Rats; D017208:Rats, Wistar; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D001555:Benzene Derivatives; D001894:Borohydrides; D004791:Enzyme Inhibitors; D016566:Organoselenium Compounds; D013438:Sulfhydryl Compounds; C469411:phenyl selenoacetylene; C061132:diphenyldiselenide; C025364:sodium borohydride; D000623:Porphobilinogen Synthase; D000114:Acetylene; D004229:Dithiothreitol