PT - JOURNAL ARTICLE AU - Jan N. M. Commandeur AU - Ioanna Andreadou AU - Martijn Rooseboom AU - Marcel Out AU - Laurens J. de Leur AU - Ed Groot AU - Nico P. E. Vermeulen TI - Bioactivation of Selenocysteine Se-Conjugates by a Highly Purified Rat Renal Cysteine Conjugate β-Lyase/Glutamine Transaminase K DP - 2000 Aug 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 753--761 VI - 294 IP - 2 4099 - http://jpet.aspetjournals.org/content/294/2/753.short 4100 - http://jpet.aspetjournals.org/content/294/2/753.full SO - J Pharmacol Exp Ther2000 Aug 01; 294 AB - 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 β-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 β-lyase/glutamine transaminase K (β-lyase/GTK) in cytosolic activity was investigated. To this end, the enzyme kinetics of 15 differentially substituted selenocysteine Se-conjugates and 11 cysteineS-conjugates was determined using highly purified rat renal β-lyase/GTK. The results demonstrate that most selenocysteine Se-conjugates are β-eliminated at a very high activity by purified β-lyase/GTK, implicating an important role of this protein in the previously reported β-elimination reactions in rat renal cytosol. As indicated by the rapid consumption of α-keto-γ-methiolbutyric acid, purified β-lyase/GTK also catalyzed transamination reactions, which appeared to even exceed that of β-elimination. The corresponding sulfur analogs also showed significant transamination but were β-eliminated at an extremely low rate. Comparison of the obtained enzyme kinetic data of purified β-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 β-elimination of selenocysteine Se-conjugates in rat renal cytosol was demonstrated. The identity and characteristics of these alternative selenocysteine conjugate β-lyases, however, remain to be established. The American Society for Pharmacology and Experimental Therapeutics