Purification and properties of Streptococcus mutans extracellular glucosyltransferase

Abstract

Extracellular glucosyltransferase (sucrose:l,6-α- o-glucan 3-α- and 6-α-glucosyltransferase) was purified about 10000-fold from the culture supernatant of Streptococcus mutans 6715. The enzyme preparation was homogeneous on polyacrylamide gel electrophoresis, isoelectric focusing and ultracentrifugation analyses. The specific activity of the enzyme was 34.9 I.U. per mg of protein and the carbohydrate content was less than 1% (w/w). The molecular weight was determined to be 149000±5000 by sedimentation equilibrlum experiment. The acidic and basic amino acids of the enzyme comprised 29 and 8.4% of total amino acid, respectively, and the isoelectric point was pH 4.1. The enzyme had the optimum pH of 5.5 and the K m value of 2.4 mM for sucrose. The water-soluble glucan, which was de novo-synthesized from sucrose by the purified enzyme, was analyzed by a gas-liquid chromatography-mass spectroscopy and was around to be l,6-α- d-glucan with highly (35%) branched structure of 1,3,6- linked glucose residue.