Some physical properties of three sugar dehydrogenases from a pseudomonad.

Recent studies of the evolution of protein molecules have been principally confined to studies of a single protein, such as hemoglobin or cytochrome c, in numerous representatives of the phylogenetic scale (1, 2). Such studies trace the changes in a protein molecule as a function of alterations of its host. A second approach would be to study the evolution of functionally related proteins by comparing their structures. Indeed, investigations of the catalytic sites of enzymes which exhibit esteratic activity have yielded interesting results (3). These latter investigations, however, suffer from interpretive limitations inherent in comparative studies of proteins from various sources; differences may be ascribed to either phylogenetic variation or to alterations in function. Such limitations in interpretation would be minimized if the proteins compared were obtained from a single species. A number of inducible sugar dehydrogenases are produced by a pseudomonad, and the regulation of these enzymes has been found to be loosely linked (4). Three of these dehydrogenases, aldose dehydrogenase, galactose dehydrogenase, and n-arabinose dehydrogenase, have been highly purified (5), and their catalytic properties have been examined (6). Some of the physical properties of the enzymes are reported here. Because of the marked catalytic similarities of the aldose and galactose dehydrogenases (B), their primary structures have been compared by means of peptide maps, and these comparisons are also reported here.