COMPLETE AMINO-ACID-SEQUENCE OF BILIVERDIN-IX-BETA REDUCTASE FROM HUMAN LIVER

The amino acid sequence of biliverdin-IXβ reductase (EC1.3.1.24) from human liver was determined by automated Edman degradation of peptides generated by enzymatic and chemical cleavages. The enzyme was a single polypeptide chain of 204 amino acid residues, and its amino acid sequence had no significant homology to that of rat liver biliverdin-IXα reductase. Biliverdin-IXα reductase from human liver had intense homology to the rat enzyme. Cysteinyl residues are essential for the enzymatic activity of biliverdin-IXα, but nonessential for that of biliverdin-IXβ reductase. The results strongly indicate that the two enzymes, biliverdin-IXα reductase and biliverdin-IXβ reductase, are distinct in enzymatic action mechanisms as well as ancient origins of gene. © 1993 Academic Press, Inc.