Levan and levansucrase of Actinomyces viscosus

Abstract

A levansucrase was demonstrated in the growth medium and in association with the cell surface of A. viscosus. The amount of enzyme produced relative to cell density is not significantly affected by the growth conditions. Sugar alcohols inhibit growth of the cells. The levansucrase hydrolyzes sucrose to produce free glucose and levan; some free fructose is also formed. There is no requirement for cofactors. The K(m) for sucrose is 12 mM. A variety of heavy metal ions and two disaccharides, lactose and cellobiose, inhibit the enzyme. The levansucrase was purified to homogeneity and has a specific activity of 90 μmol of glucose released per min per mg. The enzyme has a molecular weight of 220,000 and is composed of subunits of molecular weight 80,000. The levan product contains both β(2→1) and β(2→6) linkages. The enzyme remains tightly bound to the levan product, resulting in the formation of high molecular weight polymer on the order of 108 daltons. The possible role of the levan and levansucrase of A. viscosus in the pathogenesis of periodontal disease is discussed.