Extracellular dextranase from Streptococcus oralis.

A human dental plaque organism, Streptococcus oralis (S. mitior), was cultivated in a dextran-free, dialysed medium, and dextranase activity was isolated from the cell-free, culture supernatant. The lyophilized, crude enzyme preparation, optimum pH 6, was subjected sequentially to anion exchange and gel filtration fast protein liquid chromatography (FPLC). The dextranolytic fraction from gel filtration FPLC produced a symmetrical, baseline resolved peak. The dextranolytic enzyme was purified 1,126-fold with a yield of 2.4%. Amino acid analysis revealed a large proportion of alanine and an abundance of acidic amino acids. This extracellular enzyme isolated from S. oralis is constitutive and has a relative molecular mass of 45 kD. Further investigation of the possible structural and biochemical effects of endogenous bacterial glucanases in human dental plaques is necessary.