cDNA clones coding for hemoprotein H-450 were isolated from a rat liver cDNA library using anti-H-450 antibody. The molecular weight calculated from the deduced amino acid sequence comprising 547 amino acid residues was 60,085. The N-terminal sequence and a partial internal amino acid sequence of purified H-450, which were determined chemically, were both found in the amino acid sequence of H-450 deduced from the nucleotide sequence. H-450 mRNA is expressed in liver, kidney, and brain. A homology search of amino acid sequences indicated that H-450 shows no homology with cytochrome P-450, but shows significant homology with bacterial O-acetylserine (thiol)-lyases. However, H-450 has no O-acetylserine (thiol)-lyase activity.
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