Relationship between cell-bound dextransucrase and the agglutination of Streptococcus mutans

Dextran-induced agglutination of Streptococcus mutans cells is independent of cell-bound dextransucrase activity. Toluene extraction or the presence of Hg2+ or Cu2+ markedly decreased or completely abolished cell-bound dextransucrase activity without adversely affecting dextran-induced cell agglutination. Cells treated by heating at 100 C until cell-bound dextransucrase was completely inactivated continued to agglutinate when induced by dextran-induced cell agglutination resulted from cell treatment with trypsin and several other enzymes, as well as from ethylenediaminetetraacetic acid treatment, without a corresponding loss of cell-bound dextransucrase activity. Cells possessed a greater avidity for branched dextrans of low molecular weight than for linear dextrans of the same weight, indicating that size alone does not determine the efficiency of dextran as an inducer of agglutination. Divalent metal ions were required for both sucrose- and dextran-induced agglutination of S. mutans K1-R cells. Although normal cells of strain 6715-49 did not appear to require divalent cations for agglutination, heat- and ethlyenediaminetetraacetic acid-treated cells specifically required Ca2+. The role of Ca2+ in cell agglutination may be either to activate the cell-surface dextran receptor or to form specific intercellular Ca2+ bridges.

[Study of the cell walls of yeasts Rhodotorulamv'nfluence of the conditions of culture on the phosphatases of Rh; rubra (author's transl)]

1. Acid and alkaline phosphatase activities have been characterized on intact yeast cells and isolated cell walls Rh. rubra. These activities are sensitive to inhibition by orthophosphate. 2. The mechanical disruption does not increase the acid phosphatase activity and almost the entire activity is in the particular fraction. Its response to physicochemical factors is uniform, whatever the state of the preparation. It seemed to be entirely localized in the cell wall. The mechanical disruption of Rh. rubra yeast cells provokes only a small increase in alkaline phosphatase activity. Almost all the activity is in the particular fractions after centrifuging. The response to the physicochemical factors studied differs according to the state of the preparation. This alkaline phosphatase activity is for the most part cell wall localized, but seems also to be located in the periplasmic space or inside the plasmic membrane of Rh. rubra. 3. Trypsine or "beta-glucanase complex" treatments of the yeast cells eliminate much of peptidic and glucidic compounds and provoke a more important increase of the phosphatase activities of yeasts cultivated in rich phosphate media than that obtained after treatments of yeast cultivated in poor phosphate medium. These treatments which affect only the superficial structures of the cell envelope and do not touch the enzymic molecule (the phosphatase Km values are unchanged after treatments, and Ki values are the same before and after treatments) are favourable to a masking of the cell wall phosphatases by culture of Rh. rubra with high concentrations of phosphate. This phenomenon is corroborated by electron microscopy studies.

Glycogen synthase can use glucose as an acceptor

Glycogen synthase purified to homogeneity from rabbit skeletal muscle is essentially free of carbohydrate and shows no activity in the absence of added acceptor. It can use glucose as a substrate converting it to a glucose disaccharide in the presence of UDP-glucose as cosubstrate. The reaction is dependent on time, and on UDP-glucose, glucose, and enzyme concentrations. The product of the single step reaction co-chromatographs in two solvent systems with maltose. The glucose disaccharide produced in the reaction with UDP-[14-C]glucose and nonradioactive glucose as well as with nonradioactive UDP-glucoes and [14-C]glucose is labeled asymmetrically. The linkage is characterized as alpha-1,4 and therefore the disaccharide is identified as maltose.

[Effect of temperature on the activity of enzymes hydrolyzing non-starch polysaccharides]

The temperature optimum and thermal stability of endo-beta-glucanase, beta-glucanase, pentosanase and cellobiase from the enzymic preparations used in the brewing industry to treat high amounts of unmalted barley--citorosemin Px, citorosemin P10x, amylosubtilin G10x and brew-n-zyme--were measured. In order to determine the termerature optimum the enzyme activity was assayed under standard conditions. It was found that the temperature optimum for endo-beta-glucanase of all preparations was 50 degrees, for beta-glucanase and pentosanase--40 degrees, for cellobiase--70 degrees C. The thermal stability of endo-beta-glucanase from amylosubtilin G10x and brew-n-zyme in the aqueous solution was higher than that from ditorosemin Px and P10x. The thermal stability of the latter preparations noticeably increased in the presence of substrates.

Demonstration of a fibrillar component in the cell wall of the yeast Saccharomyces cerevisiae and its chemical nature

The ultrastructure of isolated cell walls of Saccharomyces cerevisiae from the log and stationary phases of growth was studied after treatment with the following enzymes: purified endo-beta-(1 --> 3)-glucanase and endo-beta-(1 --> 6)-glucanase produced by Bacillus circulans; purified exo-beta-glucanase and endo-beta-(1 --> 3)-glucanase produced by Schizosaccharomyces versatilis; commercial Pronase. While exo-beta-glucanase from S. versatilis had no electron microscopically detectable effect on the walls, Pronase removed part of the external amorphous wall material disclosing an amorphous wall layer in which fibrils were indistinctly visible. Amorphous wall material was completely removed by the effect of either endo-beta-(1 --> 3)- or endo-beta-(1 --> 6)-glucanase of B. circulans or by a mixture of the two enzymes. As a result of these treatments a continuous fibrillar component appeared, composed of densely interwoven microfibrils resisting further action by both of the B. circulans enzymes. The fibrillar wall component was also demonstrated in untreated cell walls by electron microscopy after negative staining. Because of the complete disappearance of the fibrils following treatment with the S. versatilis endo-beta-(1 --> 3)-glucanase it can be concluded that this fibrillar component is composed of beta-(1 --> 3)-linked glucan. Bud scars were the only wall structures resistant to the effect of the latter enzyme.

Polyphenol-protein interactions

The association of some natural and synthetic polyphenols with beta-glucosidase was examined and some observations on the chemical nature of the complex were made.