Purification and characterization of corticosteroid side chain isomerase.
Corticosteroid side chain isomerase of rat liver catalyzes the interconversion of the ketol (20-oxo-21-ol) and aldol (20-hydroxy-21-al) forms of the corticosteroid side chain. The enzyme has now been purified to apparent homogeneity from rat liver cytosol by sequential chromatography on anionic, hydroxylapatite, and gel filtration columns. Ketol-aldol isomerization is followed by measuring the exchange of tritium from 21-tritiated steroids with water. The native enzyme is a dimer of MW 44,000. The isoelectric point is 4.8 +/- 0.1 pH units. The purified enzyme is stimulated by Co3+ or Ni2+. The enzyme utilizes 11-deoxycorticosterone, corticosterone, and 17-deoxycortisol as substrate but not cortisol, tetrahydrocortisol, and prednisolone. Tritium-water exchange of (21S)-[21-3H]DOC is a pseudo-first-order reaction; 21-3H exchange from the 21R isomer proceeds with first-order kinetics only after a lag associated with its epimerization to the 21S form.
Marandici
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Population Council, New York, New York 10021.
Monder
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C
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D003035:Cobalt / Q000494:pharmacology; D003900:Desoxycorticosterone / Q000096:biosynthesis; D004795:Enzyme Stability / Q000187:drug effects; D006041:Goats; D007525:Isoelectric Focusing; D007535:Isomerases / Q000302:isolation & purification*; D007536:Isomerism; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008970:Molecular Weight; D009532:Nickel / Q000494:pharmacology; D013251:Steroid Isomerases / Q000302:isolation & purification*
D000596:Amino Acids; D003035:Cobalt; D003900:Desoxycorticosterone; D009532:Nickel; D007535:Isomerases; C047770:corticosteroid side-chain-isomerase; D013251:Steroid Isomerases