An intermediate in cyclic beta 1-2 glucan biosynthesis

Incubation of UDP-[14C]Glc with the inner membranes of Agrobacterium tumefaciens leads to the formation of cyclic beta 1-2 glucan and trichloroacetic acid-insoluble compounds. The proteolysis products of the latter show a positive charge in acid and a negative charge in alkaline buffers. The cyclic beta 1-2 glucan and the trichloroacetic acid insoluble compounds yield the same products on partial acid hydrolysis. Addition of excess non-radioactive UDP-Glc to the reaction mixture nearly stops the formation of radioactive beta 1-2 glucan and leads to a rapid fall of radioactivity in the trichloroacetic acid precipitate. Alkaline treatment of the insoluble compounds under conditions of beta-elimination leads to the partial release of free saccharides (about 30%). It is concluded that beta 1-2 glucan chains are built up joined to a protein and then released as free cyclic beta 1-2 glucan.