Alcohol dehydrogenase class I from kiwi liver has been purified, analyzed, and compared with that of other alcohol dehydrogenases. The results show that several avian and mammalian forms of the enzyme exhibit parallel evolutionary patterns in two independent lineages of a single protein, establishing a pattern in common. Furthermore, the data correlate the enzyme evolutionary pattern with that of 12S rRNA. Biologically, the patterns complement those on ratite and other avian relationships. Functionally, the enzyme has a low K m with ethanol and a branched-chain residue at position 141, like the mammalian enzymes but in contrast to the other characterized ratite enzyme (with Ala-141 and a higher K m). This pattern of natural variability suggests a frequent but not fully complete correlation between a large residue size at position 141 and tight ethanol binding.
