The purification and properties of dextransucrase from Streptococcus sanguis ATCC 10558

Dextransucrase has been purified from the culture fluids of S. sanguis 10558 by a combination of hydroxylapatite, ion-exchange, and gel-filtration steps. Two active proteins were isolated with specific activities approaching one order of magnitude higher than other preparations reported. The enzymes have mol. wt. on the order of 100 000 and exhibit pH optima between 5,8 and 6.2. In addition, detailed analysis of one of the enzymes indicates that the enzyme undergoes two ionizations that are important for activity. One pK is at 4.4 and the second at 7.4. The structures of dextrans produced by the two enzymes have been examined by p.m.r. spectroscopy, and a substantial degree of similarity was observed, with only minor differences in the proportion of alpha-(1 leads to 3) and alpha-(1 leads to 6) bonds. No evidence could be obtained that either of the enzymes was capable of catalyzing a rearrangement of alpha-(1 leads to 6) to alpha-(1 leads to 3) bonds.