Biliverdin Reductase; Substrate, Specificity and Kinetics

R B FRYDMAN; M L TOMARO; J ROSENFELD; J AWRUCH; SAMBROTTA LUIS; VALASINAS ALDONIA; FRYDMAN BENJAMIN

BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR BASIS OF DISEASE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 1987 vol. 916 p. 500 - 511

0925-4439

The substrate specificity of the different forms of rat liver biliverdin reductase was examined using synthetic biliverdins. Biliverdins carrying methyl, ethyl and one propionate residue in their structure were not substrates of biliverdin reductase. Biliverdins with one propionate and one acetate residue or with two acetate residues were not reduced by the enzyme either. The presence of two propionates in the biliverdin structure gave a biliverdin with substrate activity. Increasing the number of propionates to four, as in coprobiliverdins, did not affect substrate activity, while the octaacid urobiliverdins were also good substratesof the enzymes. The B isomer of urobiliverdin III and coprobiliverdin III were reduced at much higher rates by molecular form 3 of the enzyme as compared to molecular form 1, a fact which had already been observed with the B isomer of bfliverdius IX, XIII and hematobiliverdin. All the biliverdins mentioned above were readily reduced to bilirubins by sodium borohydride. The purified molecular forms 1 and 3 displayedsigmoidal kinetics with most of the biliverdins tested. The data were analyzed by nonlinear regression in a microcomputer and it was found that they fitted a model of a moderate cooperative dimer where both ES and ES 2 are catalytically active. The V m, K s and the Hill numbers, n H, for biliverdin IX A and B, Hematobiliverdin IX A and B, and several synthetic biliverdin isomers are given. Molecular form 2 showed classical Michaelian kinetics.