The goal of this research is to contribute to the understanding of the biochemical mechanisms of plaque formation and periodontal disease induction in man. The biosynthesis of levan will be studied in Actinomyces viscosus, a human oral bacterium which forms plaque and which produces periodontal disease in experimental animals. Enzyme in the growth medium of A. viscosus incorporates the fructose moiety, but not the glucose moiety, of labelled sucrose into high molecular weight polymer. A levansucrase has been purified to homogeneity from the growth medium (trypticase soy broth). The enzyme has a specific activity of 90 micromoles of glucose liberated from sucrose per minute per mg of protein at 25 degrees, pH 7.5, in a spectrophotometric coupled enzyme assay containing 50 mM sucrose. The enzyme has a molecular weight of 220,000, with subunits of 80,000. The enzyme is inhibited by Tris, heavy metals, lactose and cellobiose. The levan product contains both beta (2 yields 1) and beta (2 yields 6) linkages, is branched, and has a M.W. of at least 10 to the 8th power. The levan will be evaluated for its ability to 1) activate complement, 2) cause bone resorption, 3) cause bacterial cell-to-cell aggregation, 4) produce lymphocyte mitogenesis. The proposed experiments should clarify the importance of Actinomyces viscosus and levan in the pathogenesis of periodontal disease, and may suggest strategies for the prevention of periodontal disease in man.