Biliverdin-IX alpha reductase and biliverdin-IX beta reductase from human liver. Purification and characterization.

摘要: This report describes for the first time identification of four forms biliverdin reductase including two biliverdin-IX beta reductases and alpha reductases, designated isozymes I II III IV, respectively, in human liver cytosolic fractions. The were purified to homogeneity. There was a 7,800-15,000-fold increase specific activity when compared with crude preparation, recovery 8-26%. enzymes monomers molecular weight about 21,000 (isozymes II) 34,000 IV). strictly biliverdin, no other oxidoreductase activities detected preparations. used NADPH NADH as electron donors reduction biliverdin. apparent Km values I, II, III, IV 35.9, 13.1, 10.9, 34.1 microM, whereas those 5.6, 8.2, 7.9, 23.4 mM, respectively. It assumed that rather than physiological donor intracellular value system 0.3 microM 1.0 0.8 Isozymes beta, -IX gamma, delta substrates but not alpha, preferred most effective substrate among isomers. NADPH-dependent enzyme inhibited by concentrations excess 3-4 microM. activities, especially sensitive SH reagents iodoacetamide, p-chloromercuribenzoic acid, N-ethylmaleimide. optimum pH reaction 8.2 7.4. proportion total considerably higher fetal adult liver.