Germaine et al. [1][2][3] showed that the addition of dextran to Streptococcus mutans dextransucrase digests increased the rate of dextran synthesis. They found that the rate was dependent on the size of the dextran chain and reached a maximum when the average size of the added dextran was 30 glucose residues. The glucansucrases elaborated by Streptococci are constitutive and are produced by the organisms when grown in glucose, fructose, or mannitol media [ 4 ]. Sucrose is not required in the medium for elaboration of the enzyme (s) and hence dextran is not produced along with the dextransucrase in the culture supernatant.
Kobayashi and Matsuda [5,6] also reported that purified dextransucrases elaborated by both Leuconostoc mesenteroides B-512F and Strepwcoccus sp. were stimulated by the addition of dextran, although both enzymes could synthesize dextran without the addition of dextran to the digests. The rate of dextran synthesis in dextran-free digests was accompanied by a lag-period that could be eliminated by the addition of exogenous dextran.
Both Germaine et al. [1][2][3] and Kobayashi and Matsuda [7] interpreted their data as evidence for a primer-based mechanism for dextran synthesis. This mechanism had been assumed for the synthesis of dextran in the 1940's, 50's and early 60's [8--11] and was based primarily by analogy with the studies of Cori and Cori [ 12] and Swanson and Cori [ 13] on glycogen phosphorylase and Hanes [ 14] on potato starch phosphorylase. In these studies it was shown that glucose residues were added from a-D-glucose 1-phosphate to the nonreducing glucose residues of glycogen and starch. The reaction did not take place unless a glycogen primer chain or a starch primer chain was present. It, thus, resulted that a primer