Complete amino acid sequence of biliverdin-IX beta reductase from human liver.

The amino acid sequence of biliverdin-IX beta 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-IX alpha reductase. Biliverdin-IX alpha reductase from human liver had intense homology to the rat enzyme. Cysteinyl residues are essential for the enzymatic activity of biliverdin-IX alpha, but nonessential for that of biliverdin-IX beta reductase. The results strongly indicate that the two enzymes, biliverdin-IX alpha reductase and biliverdin-IX beta reductase, are distinct in enzymatic action mechanisms as well as ancient origins of gene.