Purification and Properties of Extracellular Glucosyltransferase Synthesizing 1,3-α-d-Glucan from Streptococcus mutans Serotype α

SUMMARY: Extracellular 1,3-α-d-glucan synthase (sucrose: 1,3-α-d-glucan 3-α-d-glucosyltransferase, EC 2.4.1. -) of Streptococcus mutans HS6 (serotype a) was purified from culture supernatant by ultrafiltration, DEAE-Sepharose chromatography and preparative isoelectric focusing. The enzyme had a molecular weight of 158000 by SDS-PAGE and an isoelectric point of pH 5·2. The specific activity of the enzyme was 48·3 i.u. (mg protein)-1. The K m for sucrose was 1·2 mM and the activity was optimal at pH 6·0. The enzyme activity was stimulated about 20-fold in the presence of dextran T10. Glucan was synthesized de novo from sucrose by the enzyme and characterized as a linear 1,3-α-d-glucan by GC-MS.