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The recently determined primary structure of glucose dehydrogenase from ~a~i~~as megater~~m was scanned by computerized comparisons for similarities with known polyol and alcohol dehydrogenases. The results revealed a highly significant similarity between this glucose dehydrogenase and ribitol dehydrogenase from Klebsiella aerogenes. Sixty-one positions of the 262 in glucose dehydrogenase are identical between these two proteins (23% identity), fitting into a homology alignment for the complete polypeptide chains. The extent of similarity is equivalent to that between other highly divergent but clearly related dehydrogenases (two zinc-containing alcohol dehydrogenases, 25%; sorbitol and zinc-containing alcohol dehydrogenases, 25%; ribitol and non-zinc-containing alcohol dehydrogenases, 20%), and suggests an ancestral relationship between glucose and ribitol dehydrogenases from different bactera. The similarities fit into a previously suggested evolutionary scheme comprjsing short and long aIcohol and polyol dehydrogenases, and greatly extend the former group to one composed of non-zinc-containing alcoholpolyol-glucose dehydrogenases.

The amino acid sequence of glucose dehydrogenase from Bacillus megaterium has been determined. The enzyme consists of 4 identical subunits, each containing 262 amino acid residues. Its structure was established using manual Edman degradation procedures after modification of the enzyme in the native form with reagents specific to the amino acids histidine, tyrosine, tryptophan and lysine in order to identify residues involved in catalysis or located in the subunit binding area. Glucose dehydrogenase Dehydrogenase Modification Bacillus megateriumAmino acid sequence

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