Different forms of quinoprotein aldose-(glucose-) dehydrogenase in Acinetobacter calcoaceticus

The ratios of the oxidation rates of aldose sugars, determined in cell-free extracts of Acinetobacter calcoaceticus, vary with the strain and growth conditions used. Three distinct forms of glucose dehydrogenase with different substrate specificities, occurring in variable proportions in these extracts, are responsible for this effect. One form is the already known "soluble glucose dehydrogenase", the other two forms are complexes containing enzyme and components of the respiratory chain. The proportions in which the enzyme forms are found in the cell-free extract correlate with the oxidative behaviour of whole cells with respect to aldose sugars, It is concluded, therefore, that the enzyme forms are not an artefact of the isolation procedure but that they exist as such in vivo. Since the two complexes can be converted into the soluble enzyme form, aldose dehydrogenase can, probably, be integrated in three different ways into the respiratory chain. The presence of glucose during growth does not stimulate aldose dehydrogenase production. This is not surprising since the enzyme has no function is carbon metabolism, except perhaps in strains growing on pentoses at high pH. Therefore, the physiological role of quinoprotein aldose dehydrogenase in this organism may be primarily in energy generation.