Metabolism of sucrose by Streptococcus sanguis 804 (NCTC 10904) and its relevance to the oral environment

Darlington, William (1978) Metabolism of sucrose by Streptococcus sanguis 804 (NCTC 10904) and its relevance to the oral environment. PhD thesis, University of Glasgow.

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The extracellular glucosyltransferases of Streptococcus sanguis polymerise the glucosyl moiety of sucrose to form high molecular weight complex glucans.
The adhesive and agglutinative properties of these glucans are important in the formation of dental plaque and, hence, in cariogenesis.
The glucosyltransferases of S. sanguis 804 (NCTC) were extensively purified (182-fold) by hollow fibre ultrafiltration (Bio-Fiber 80) followed by ammonium sulphate precipitation (0–70% of saturation). The enzymes were further purified by hydroxylapatite chromatography and appeared by this technique to consist of at least three enzymes with differing specific activities.
It is not known whether these enzymes are, in fact, composed of different polypeptides or are modified forms of one protein.
The activity of the glucosyltransferases can be measured as the rate of release of fructose from sucrose or as the rate of synthesis of ethanol-sodium acetate-precipitable polysaccharide (glucan). Using the former method, Kapp for sucrose for (NH4) 2SO4-purified glucosyltransferases was about 6 mmol/l and, using the latter method, Kapp was about 20 mmol/l.
Glucosyltransferase activity (as rate of glucan synthesis) was stimulated 2 to 4-fold by low concentrations (0.125-0.50 μmol/l) of T2000 Dextran (Pharmacia; mol. wt. 2 × 106). Glucan synthesis was inhibited slightly by nigerose and was inhibited strongly by metrizamide (85% inhibition at 170 μmol/l metrizamide). The rate of release of fructose was not affected by either xylitol or hydrogen peroxide.
The rate of synthesis of precipitable glucan was strongly inhibited by high concentrations of substrate (sucrose); the rate of release of fructose was relatively unaffected.
The proposed mechanism for this effect is that sucrose acts as an alternative glucosyl acceptor (as well as donor) and thus inhibits glucosyl transfers to growing glucan chains.
The oral concentrations of sucrose during and after consumptions of various sweet foods and beverages were studied and were often sufficient to inhibit glucan synthesis. In such cases, the sucrose concentrations for maximum rate of glucan synthesis only occurred as sucrose was cleared from the mouth, after the food or drink was finished. Glucan synthesis by S. sanguis is important in plaque formation. Thus, these results provide an additional explanation for the clinical finding that the incidence of caries is related to the frequency of dietary intake of sucrose and not merely the total amount of sucrose consumed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Caries, dental plaque. streptococcus sanguis, streptococcus sanguinis, glucosyltransferase, sucrose.
Subjects: Q Science > QD Chemistry
Q Science > QH Natural history > QH345 Biochemistry
R Medicine > RK Dentistry
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Beeley, Doctor Josie A.
Date of Award: 1978
Depositing User: Mrs Marie Cairney
Unique ID: glathesis:1978-7017
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 08 Jan 2016 14:30
Last Modified: 07 Jun 2017 08:29

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