Levan and levansucrase of Actinomyces viscosus

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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 Km for sucrose is 12 mM. A variety of heavy metal ions and 2 disaccharides, lactose and cellobiose, inhibit the enzyme. The levansucrase was purified to homogeneity and has a specific activity of 90 .mu.mol of glucose released/min per mg. The enzyme has a MW of 220,000 and is composed of subunits of MW 80,000. The levan product contains .beta.(2 .fwdarw. 1) and .beta.(2 .fwdarw. 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.