4 GLUCOSYLTRANSFERASES, GTFJ, GTFK, GTFL AND GTFM, FROM STREPTOCOCCUS-SALIVARIUS ATCC-25975

The four recombinant glucosyltransferases (GTFs), GtfJ, GtfK, GtfL and GtfM, that had previously been cloned from Streptococcus salivarius A TCC 25975, were individually expressed in Escherichia coli and their g lucan products and kinetic properties were analysed. GtfJ was a primer -dependent GTF which synthesized an insoluble glucan composed mainly o f alpha-(1 --> 3)-linked glucosyl residues in the presence of dextran T-10. GtfK was primer-stimulated, and produced a linear soluble dextra n without any detectable branch points both in the absence and in the presence of dextran T-10. GtfL was primer-independent and produced a m ixed-linkage insoluble glucan composed of approximately equal proporti ons of alpha-(1 --> 3)- and alpha-(1 --> 6)-linked glucosyl residues. GtfL was inhibited by dextran T-10. GtfM was primer-independent and pr oduced a soluble dextran with approximately 5 % alpha-(1 --> 3)-linked glucosyl residues. GtfM was essentially unaffected by the presence of dextran T-10. The results confirmed that each enzyme represented one of the four possible combinations of primer-dependency and product sol ubility and that each possessed unique biosynthetic properties. The so luble dextrans formed by GtfK end GtfM, as well as the mixed-linkage i nsoluble glucan formed by GtfL, were also capable of acting as primers for the primer-dependent GtfJ and the primer-stimulated GtfK. Unexpec tedly, the linear dextran produced by GtfK was by far the least effect ive either at priming itself or at activating and priming the primer-d ependent GtfJ.