Bioactivation of selenocysteine Se-conjugates by a highly purified rat renal cysteine conjugate beta-lyase/glutamine transaminase K.
Selenocysteine Se-conjugates have recently been proposed as potential prodrugs to target pharmacologically active selenol compounds to the kidney. Although rat renal cytosol displayed a high activity of beta-elimination activity toward these substrates, the enzymes involved in this activation pathway as yet have not been identified. In the present study, the possible involvement of cysteine conjugate beta-lyase/glutamine transaminase K (beta-lyase/GTK) in cytosolic activity was investigated. To this end, the enzyme kinetics of 15 differentially substituted selenocysteine Se-conjugates and 11 cysteine S-conjugates was determined using highly purified rat renal beta-lyase/GTK. The results demonstrate that most selenocysteine Se-conjugates are beta-eliminated at a very high activity by purified beta-lyase/GTK, implicating an important role of this protein in the previously reported beta-elimination reactions in rat renal cytosol. As indicated by the rapid consumption of alpha-keto-gamma-methiolbutyric acid, purified beta-lyase/GTK also catalyzed transamination reactions, which appeared to even exceed that of beta-elimination. The corresponding sulfur analogs also showed significant transamination but were beta-eliminated at an extremely low rate. Comparison of the obtained enzyme kinetic data of purified beta-lyase/GTK with previously obtained data from rat renal cytosol showed a poor correlation. By determining the activity profiles of cytosolic fractions applied to anion exchange fast protein liquid chromatography and gel filtration chromatography, the involvement of multiple enzymes in the beta-elimination of selenocysteine Se-conjugates in rat renal cytosol was demonstrated. The identity and characteristics of these alternative selenocysteine conjugate beta-lyases, however, remain to be established.
Commandeur
J N
JN
Leiden/Amsterdam Center for Drug Research, Division of Molecular Toxicology, Department of Pharmacochemistry, Vrije Universiteit Amsterdam, The Netherlands. command@chem.vu.nl
Andreadou
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Rooseboom
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Out
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de Leur
L J
LJ
Groot
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Vermeulen
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NP
D000818:Animals; D000838:Anions; D001711:Biotransformation; D013437:Carbon-Sulfur Lyases / Q000302:isolation & purification / Q000378:metabolism*; D002850:Chromatography, Gel / Q000379:methods; D002852:Chromatography, Ion Exchange / Q000379:methods; D003600:Cytosol / Q000201:enzymology; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D008190:Lyases / Q000302:isolation & purification / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017279:Selenocysteine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics*; D013379:Substrate Specificity; D000637:Transaminases / Q000302:isolation & purification / Q000378:metabolism*
D000838:Anions; D017279:Selenocysteine; D000637:Transaminases; C427605:glutamine - phenylpyruvate transaminase; C021481:kynurenine-oxoglutarate transaminase; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase