Soluble glucan synthesis catalyzed by dextransucrase preparations from Streptococcus mutans 6715 were inhibited by pyridoxal-5-phosphate and several other pyridine analogs, including pyridoxine, pyridoxamine, pyridoxamine-5-phosphate, pyridoxal, and 4-pyridoxic acid. Pyridine and pyridine-4-carboxaldehyde were not effective inhibitors of the enzyme. Kinetic analyses suggested that pyridoxal-5-phosphate is a noncompetitive inhibitor of dextransucrase. The inactivation was dependent on time, pyridoxal-5-phosphate concentration, and hydrogen ion concentration. Apparent Ki values were 4.9 mM at pH 7.0 and 4.2 mM at pH 5.5. Dextransucrase activity could be restored by dialysis to remove the inhibitors. Maximum inhibition was observed after a 120-min incubation of the enzyme with pyridoxal-5-phosphate. The pH optima for inhibition by pyridoxal-5phosphate were 4 and 7. The sucrose-dependent adherence of S. mutans cells to saliva-coated hydroxylapatite beads was also inhibited by pyridoxal-5-phosphate but only marginally by the other pyridine analogs. In addition, pyridoxal-5phosphate markedly reduced the rate of acid production by intact S. mutans cells from sucrose or glucose substrates. Another pyridoxal-5-phosphate analog, 2methyl-5-hydroxypyridine, was also effective in preventing the production of acid by S. mutans from sucrose or glucose. When S. mutans cells were preincubated with pyridoxal-5-phosphate or pyridine analogs, significant reductions in the rate of D-glucose uptake were observed. It is suggested that the inhibition of dextransucrase occurs because of a change in enzyme conformation which results from the binding of the pyridine derivatives. The results suggest that pyridoxal-5phosphate or structural analogs may ultimately be useful in reducing the incidence of dental caries. Streptococcus mutans is a name given to a group of oral bacteria believed to be involved in
Steroids U 0300Bone Selective Effect of an Estradiol Conjugate with a Novel Tetracycline-Derived Bone- Targeting Agent. -The novel substance (I) shows a partial separation of the skeletal effects of estradiol from the uterine effects in an osteoporosis model. The results are discussed in detail. -(NEALE, J. R.; RICHTER, N. B.; MERTEN, K. E.; TAYLOR, K. G.; SINGH, S.; WAITE, L. C.; EMERY, N. K.; SMITH, N. B.; CAI, J.; PIERCE*, W. M.
The glucan-binding lectin (GBL) of Streptococcus sobrinus is cell associated, enabling the bacteria to be aggregated by alpha-1,6 glucans. Glucans, such as amylose, pullulan, laminarin and nigeran, have no affinity for the lectin. High molecular weight alpha-1,6 glucans (dextrans) readily aggregate the bacteria, whereas low molecular weight glucans inhibit the aggregation brought about by the high molecular weight species. Methylated glucan T-2000 (an alpha-1,6 glucan with an average molecular weight of 2 x 10(6) Da) aggregated the bacteria very poorly when the extent of methylation (DS, or degree of substitution) was high, and less poorly when the DS was low. Similarly, methylated low molecular weight alpha-1,6 glucan was a poor inhibitor of aggregation induced by the high molecular weight glucan T-2000. Because the methylation occurred primarily on the hydroxyl of C-2, it is suggested that the hydroxyl is needed for formation of the lectin-glucan complex. It appears that the GBL is not only stereospecific in interaction with glucans, but also regio-specific, interacting only with the underivatized alpha-1,6-glucan.
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