BIOSYNTHESIS OF BETA-D-GLUCAN OF SCLEROTIUM ROLFSII SACC . DIRECTION OF CHAIN PROPAGATION AND INSERTION OF BRANCH RESIDUES

The polysaccharide produced by the mold Sclerotium rolfsii Sacc. lends itself to studies of in vivo biosynthesis, since means are available to degrade pulse-labeled polysaccharide and determine the specific activity of all of the types of D-glucose residue present in its structure. Studies of this kind show, by direct measurement of the specific activities of the reducing and nonreducing terminals, that the direction of chain elongation is toward the nonreducing terminal. They show further that the interbranch, branch-point, and branch D-glucose residues are inserted into the structure of the molecule at about the same point in time, and that the D-glucose residues go intact into the structure, with no rearrangement of the carbon chain. The significance of these observations to the route of biosynthesis of the polysaccharide is discussed. © 1969.