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D C Ellwood

Publications and source records attributed to D C Ellwood.

12 recordsLinked to original sources
PubMed1979

Effect of growth rate and glucose concentration on the activity of the phosphoenolpyruvate phosphotransferase system in Streptococcus mutans Ingbritt grown in continuous culture.

Streptococcus mutans Ingbritt was grown anaerobically in a chemostat with a glucose limitation, as well as with an excess of glucose (amino acid limitation) at dilution rates (D) between 0.05 and 0.4 h(-1) (mean generation time = 12 to 1.5 h). The glucose-limited culture produced cells having 1.5- to 6.0-fold greater glycolytic activity than the cells from the glucose-excess culture. The preferred substrate for these cells was glucose, with the glycolytic rate for sucrose being only slightly lower; the rate for fructose was half that of glucose. The glycolytic rate of the glucose-limited cells was maximum at D = 0.1 h(-1), with a decline in rate as the growth rate approached D = 0.4 h(-1). A comparison of the activity of phosphoenolpyruvate phosphotransferase system (PTS) in the two types of cells showed that the glucose-limited cells had 1.7- to 5.6-fold greater PTS activity for the three sugars than the glucose-excess-grown cells. Whereas little difference was seen between the three sugars with the latter cells, the glucose-PTS had the greatest activity with glucose-limited cells, with the maximum in cells grown at D = 0.1 h(-1). Comparison of the rate of sugar uptake in the chemostat with the rate of PTS transport activity in the cells at each growth rate demonstrated that only under conditions of slow growth with a glucose limitation was the PTS system capable of supporting growth on glucose. Furthermore, PTS activity in cells grown with an excess of glucose was insignificant when compared with glucose uptake during growth in the chemostat. This evidence supports the observation that S. mutans possesses at least one other system, in addition to the PTS, for the transport of glucose into the cell. The organism was, however, devoid of glucose-proton symport transport activity.

Biological Transport, Active↗
PubMed1979

Effect of growth rate and glucose concentration on the biochemical properties of Streptococcus mutans Ingbritt in continuous culture.

A comparison was made of the properties of Streptococcus mutans Ingbritt grown in continuous culture under conditions of excess glucose (nitrogen limitation) and limiting glucose at mean generation times of 1.7 to 14 h. Only low levels of glucoamylase-specific glycogen were formed in cells from either culture, and the total carbohydrate content of the cells under excess glucose was only at most 1.6-fold higher than in the glucose-limited culture. A negligible amount of cell-free polysaccharide was formed in either culture, although a significant level of glucosyltransferase activity was observed in both, with the highest activity at D = 0.2 and 0.4 h(-1) with a glucose limitation. Other differences were observed. (i) Lactate was the main end product of the glucose-excess culture, whereas acetate, formate, and ethanol were the main products of the glucose-limited culture except at a mean generation time of 1.5, when lactate represented 30% of the products. (ii) The yield (in grams per mole of glucose) of the latter culture was 2.6- to 4.0- fold higher than the yield of the glucose-excess culture. (iii) Washed cells from the glucose-limited culture were much more acidogenic (1.7- to 6.2-fold) than the glucose-excess cells when incubated with glucose, sucrose, and fructose. Endogenous glycolytic activity by the latter cells was significant, being 31 to 92% of the exogenous glucose rate at the four dilution rates. (iv) Cells from the glucose-excess culture were more insensitive to fluoride than cells from the glucose-limited culture. The NaF 50% inhibition dose values for the effect of fluoride on the metabolism of glucose, sucrose, and fructose were calculated for the four dilution rates at four pH values. This analysis indicated that rapidly metabolizing cells were more sensitive to fluoride than cells that metabolized the sugars more slowly.

Acetates↗
PubMed1979

Change from homo- to heterolactic fermentation by Streptococcus lactis resulting from glucose limitation in anaerobic chemostat cultures.

Lactic streptococci, classically regarded as homolactic fermenters of glucose and lactose, became heterolactic when grown with limiting carbohydrate concentrations in a chemostat. At high dilution rates (D) with excess glucose present, about 95% of the fermented sugar was converted to l-lactate. However, as D was lowered and glucose became limiting, five of the six strains tested changed to a heterolactic fermentation such that at D = 0.1 h(-1) as little as 1% of the glucose was converted to l-lactate. The products formed after this phenotypic change in fermentation pattern were formate, acetate, and ethanol. The level of lactate dehydrogenase, which is dependent upon ketohexose diphosphate for activity, decreased as fermentation became heterolactic with Streptococcus lactis ML(3). Transfer of heterolactic cells from the chemostat to buffer containing glucose resulted in the nongrowing cells converting nearly 80% of the glucose to l-lactate, indicating that fine control of enzyme activity is an important factor in the fermentation change. These nongrowing cells metabolizing glucose had elevated (ca. twofold) intracellular fructose 1,6-diphosphate concentrations ([FDP](in)) compared with those in the glucose-limited heterolactic cells in the chemostat. [FDP](in) was monitored during the change in fermentation pattern observed in the chemostat when glucose became limiting. Cells converting 95 and 1% of the glucose to l-lactate contained 25 and 10 mM [FDP](in), respectively. It is suggested that factors involved in the change to heterolactic fermentation include both [FDP](in) and the level of lactate dehydrogenase.

Acetates↗
PubMed1978

Effects of fluoride on carbohydrate metabolism by washed cells of Streptococcus mutans grown at various pH values in a chemostat.

Streptococcus mutans Ingbritt was grown anaerobically in a chemostat, at a rate (mean generation time, 13 h) similar to that in dental plaque, in a complex medium with excess glucose and at pH values of 6.5, 6.0, and 5.5. The yield of cells was constant at pH 6.5 and 6.0 (2.00 mg/ml) but fell to 1.25 at pH 5.5; Y(glucose) was relatively constant under all conditions. Lactic acid was the major end product. Amino acid analysis of the culture supernatants indicated that growth was probably limited by the availability of cysteine. Cells were harvested and monitored for their capacity to produce acid from endogenous polysaccharide and exogenous sugars in the presence and absence of NaF, as well as for their glucose phosphoenolpyruvate (PEP)-phosphotransferase activity. Surprisingly, cells grown at pH 5.5 possessed two to three times more glycolytic activity, as measured by the rate of acid production, than cells grown at pH 6.5 and 6.0 when incubated in a washed suspension at constant pH with a sugar source. Furthermore, the cells grown at pH 5.5 were about twice as resistant to the effect of NaF in reducing the rate of acid production in this system. Fluoride inhibition could be reversed by increasing the pH of the system. Cells grown at all three pH values showed significant acid production from endogenous reserves, despite the fact that the glucoamylase-specific glycogen content of the cells dropped from 33% of the total carbohydrate during pH 6.5 growth to only 3% after growth at pH 6.0 and 6.5. Incubation of washed cells for 18 h in phosphate buffer resulted in the loss of 62% of the total carbohydrate, indicating that nonglycogen cellular polysaccharide was metabolized. A comparison of the fluoride effect on endogenous and exogenous metabolism under pH fall conditions showed that, with pH 6.5- and 6.0-grown cells, the inhibitor was more effective in the presence of an exogenous carbon source than in its absence. This effect was not seen with pH 5.5-grown cells. The decreased sensitivity of the pH 5.5-grown cells to fluoride was probably associated with the decreased glucose PEP-phosphotransferase activity (11%) in these cells compared with the activity of those grown at pH 6.5. This evidence supports the hypothesis that S. mutans possesses at least two glucose transport systems, one of which is relatively fluoride insensitive.

Amino Acids↗
PubMed1977

Enhanced plasma persistence of therapeutic enzymes by coupling to soluble dextran.

Conjugation of carboxypeptidase G and arginase, two enzymes of therapeutic interest, to a soluble dextran significantly enhanced plasma persistence in normal and tumour-bearing mice. A prolonged decrease in arginine concentrations in plasma of tumour-bearing mice was demonstrated by using the dextran-linked arginase. Gel filtration of dextran-enzyme conjugate showed that enzyme activity co-chromatographed as a single peak with carbohydrate, and enzyme was shown to be covalently linked to the dextran.

Animals↗
PubMed1976

Variations in surface polymers of Streptococcus mutans.

The cell wall composition of strains of S mutans with respect to sugars and proteins appears to be correlated to the serological grouping although groups c and E are rather similar. There also appear to be similarities in the structure of the polysaccharide formed by the glycosyltransferases from organisms of serological groups b and d. However, the activity of these enzymes appears to be variable in these groups. The most noteworthy difference found was that between the three Ingbritt strains. All three strains gave identical results with regard to their cell wall composition, and presumably this would mean that they were identical serologically. However, Ingbritt LH differed considerably from both the others in the types of polysaccharide formed by their glycosyltransferases from sucrose. Ingbritt B was a reisolate from monkeys, whereas Ingbritt LH was maintained in laboratory culture, and this may explain the difference. Clearly, more work will be required to explain this difference and as c strains are commonly isolated from plaque, it would seem desirable to clear up this point.

Cell Wall↗
PubMed1975

The amino acid pool of Hansenula holstil: characterisation, and changes mediated by environment.

Amino acid pools extracted from Hansenula holstii grown in continuous culture with either ammonia or nitrate as sole source of nitrogen, under a variety of substrate limitations, were characterised and quantified. Pools from corresponding cultures were shown to be similar in size and composition, regardless of whether ammonia or nitrate was the nitrogen source. Large changes in pools (both quantitative and qualitative) occurred when cultures were grown under different substrate limitations. Such changes were particularly large in glutamate, glutamine, alanine, lysine and arginine; the possible significance of such environment-mediated changes is discussed.

Amino Acids↗