Structural studies of alcohol dehydrogenase from rat liver.

Abstract

The amino acid composition of alcohol dehydrogenase from rat liver was determined. Tryptic peptide maps of the carboxymethylated protein were compared with those of the corresponding derivative of the horse enzyme. Large peptides, not ordinarily resolved by this method, were redigested with thermolysin or chymotrypsin to permit a comparison of the entire proteins. The amino acid sequences of peptides of special interest were determined.A subunit molecular weight close to 40000 is established for rat liver alcohol dehydrogenase. The protein is homologous to the corresponding equine and human enzymes; sequence analysis of about one‐fifth of all residues in the protein chain of the rat enzyme shows a structural identity of about 80% among the subunits of the enzymes from man, horse and rat. The rate of evolution in alcohol dehydrogenase is estimated. Species differences of special structural or functional interest include exchanges of cysteine residues and of amino acids adjacent to the “active‐site” cysteine residue.No evidence was detected for subunits of different primary structures in rat liver alcohol dehydrogenase; neither the subunit differences characteristic for the human nor for the equine isoenzymes were found. It thus seems as if isoenzymes of liver alcohol dehydrogenase have evolved independently in these three species.