D-sorbitol-6-phosphate dehydrogenase from Lactobacillus casei.

Several different systems for the conversion of sorbitol to hexose have been described in microorganisms. In the pseudomonads, sorbitol may be oxidized to fructose (Shaw, 1956) or to sorbose (Sebek and Randles, 1952). The latter investigators concluded that the conversion of sorbitol to fructose or sorbose did not involve phosphorylation since carbon dioxide was not liberated from bicarbonate buffer upon incubabation of whole cells, adenosine triphosphate, and hexitol. Cell-free preparations of Acetobacter suboxydans have been shown to dissimilate sorbitol by three different pathways. In addition to a dehydrogenase, presumably a flavoprotein which catalyzes the oxidation of sorbitol to hexose (Widmer et al., 1956; Arcus and Edson, 1956) two alternate enzyme systems found in the soluble portions of the cells have been described (Cummins et al., 1957a). Separation of these systems revealed the existence of a DPN3and a TPN-linked sorbitol dehydrogenase (Cummins et al., 1957b). The product of the DPN-linked oxidation was found to be fructose whereas the latter formed sorbose. Studies by Wolff and Kaplan (1956a) demonstrated that D-sorbitol-6-phosphate is dehydrogenated by cell-free extracts of Escherichia coli strain B. The phosphorylated route was indicated as the major pathway of sorbitol dissimilation since the specific activity of extracts of sorbitol-grown cells was approximately 60-fold greater for sorbitol-6-phosphate as compared to sorbitol. The results presented in this paper describe the isolation, purification, and properties of a DPN-linked enzyme from Lactobacillus casei