Evolution
Genetic evidence from comparisons of multiple organisms, showed that a glutathione-dependent formaldehyde dehydrogenase, identical to a class III alcohol dehydrogenase (ADH-3/ADH5), probably is the ancestral enzyme for the entire ADH family. Early on in evolution, an effective method for eliminating both endogenous and exogenous formaldehyde was important and this capacity has conserved the ancestral ADH-3 through time. From genetic duplications of ADH-3, followed by series of mutations, the other ADHs evolved. The ability to produce ethanol from sugar is believed to have initially evolved in yeast. This feature is not adaptive from an energetic point of view, but by making alcohol in such high concentrations so that they were toxic to other organisms, yeast cells could effectively eliminate their competition. Since rotting fruit can contain more than 4% of ethanol, animals eating the fruit needed a system to metabolize exogenous ethanol. This was thought to explain the conservation of ethanol active ADH in other species than yeast, though ADH-3 is now known to also have a major role in nitric oxide signaling.
Read more about this topic: Alcohol Dehydrogenase
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