The Biosynthesis and Metabolism of Polyols

Experiments involving the photosynthetic assimilation of [14C]carbon dioxide by plum leaves (Prunus domestica, var. Victoria) have indicated that D-glucitol (I) (sorbitol), the acylic polyol of these leaves, plays an important role in their metabolism (Anderson, Andrews & Hough, 1961). With leaves previously kept in the dark for 24 hr. a higher proportion of the incorporated 14C was utilized for sorbitol synthesis than for starch synthesis. Further, under natural conditions the concentration of glucitol in the leaves did not alter during the course of a day. The close structural relationship between Dglucose and D-glucitol suggests their ready interconversion when they occur together in Nature. To investigate this possibility, D-[1-14C]and D[6-14C]-glucose were metabolized by plum leaves and the resultant labelling in D-glucitol was determined. D-[1-_4C]Glucitol was also fed to plum leaves in an attempt to detect the main pathways of glucitol metabolism. In addition, the labelling in D-glucitol after metabolism of D-[6-14C]glucuronic acid by plum leaves was examined. Two chemical procedures have been developed for the degradation of D-[14C]glucitol to determine the labelling at some of the individual carbon atoms. They are outlined in Schemes 1 and 2.