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The presence of sucrose synthetase and sucrose phosphate synthetase has been demonstrated in two species of green algae: Chlorella vulgaris and Scenedesmus obliquus. Partial purification from crude extracts allowed the determination of the kinetic constants of algae enzymes. They are very similar to the ones reported for enzymes from higher plants.
Ten men and nine women ages 35 to 55 consumed two diets for 6 weeks each in a cross-over design. The diets were composed of identical natural foods and 30% of the calories as either sucrose or wheat starch. Carbohydrate, fat, and protein supplied 43, 42, and 15% of the calories, respectively. Of the calories 10% was eaten at breakfast (7:00 to 8:30 AM) and 90% at dinner (4:30 to 6:30 PM). Inital body weights were essentially maintained. Fasting serum insulin and glucose levels were significantly higher with the sucrose than with the starch diet. The insulin response and the insulin:glucose ratios after a sucrose load (2 g/kg body weight) were greater after the subjects consumed the sucrose diet. Sucrose feeding produced increases in fasting serum insulin, the insulin:glucose ratio and the insulin response to a sucrose load that were of greater magnitude in a subgroup of nine subjects classified as potentially carbohydrate-sensitive than in normal subjects. Glucose response to a sucrose load and fasting serum glucagon did not differ significantly with diet. Fasting insulin and glucose showed significant increases as a function of time on diet. These results indicate that sucrose feeding produces undersirable changes in several of the parameters associated with glucose tolerance.
The Lactococcus lactis sucrose operon was located on the conjugative transposon Tn5276 and the nucleotide sequence of the sacA gene, encoding sucrose-6-phosphate hydrolase, and its surrounding regions was determined. Northern blot analysis showed that the sucrose operon contains two divergent transcriptional units of 3.2 and 3.6 kb, the expression of which is considerably higher in cells grown on sucrose than in cells grown on glucose. This was confirmed by primer extension studies which demonstrated that transcription is initiated at two sucrose-inducible promoters with a back-to-back organization. The 3.2-kb transcriptional unit includes the sacB gene which most probably encodes the sucrose-specific enzyme II of the phosphotransferase system, and may contain the gene encoding fructokinase. The 3.6-kb transcriptional unit includes genes sacA and sacR. The protein encoded by the sacR gene is likely to be involved in the regulation of the sac operon expression, since its deduced N terminus is homologous to helix-turn-helix DNA-binding domains found in several regulatory proteins.
The adjacent sacX and sacY genes are involved in sucrose induction of the Bacillus subtilis sacB gene by an antitermination mechanism. sacB, encoding the exoenzyme levansucrase, is also subject to regulation by the DegS-DegU signalling system. Using sacXY'-lacZ and sacX'-lacZ fusions, we show that the transcription of the sacX and sacY genes is both inducible by sucrose and regulated by DegU. sacX and sacY appear to constitute an operon, since the deletion of the sacX leader region abolished the expression of a sacXY'-lacZ fusion. The degU-dependent promoter was located by deletion analysis and reverse transcriptase mapping 300 nucleotides upstream from the sacX initiator codon. Sucrose induction of the sacX'-lacZ fusion requires either SacY or the homologous SacT antiterminator, which is involved in sucrose induction of the intracellular sucrase gene (sacPA operon). Sequence analysis of the sacX leader region revealed (20 nucleotides downstream from the transcription start site) a putative binding site for these regulators; however, no structure resembling a rho-independent terminator could be found overlapping this site, unlike the situation for sacPA and sacB. Deletion of a segment of the leader region located 100 nucleotides downstream from this site led to constitutive expression of the sacXY'-lacZ and sacX'-lacZ fusions. These results suggest that the mechanism of sucrose induction of sacXY is different from that of sacPA and sacB.
The behaviour of rumen ciliates in culture in vitro is studied according to the concentration of substrates and requirements of middle removal. The most favorable concentrations, for a best ciliate's survival is from 0.4 to 0.6 mg/ml of sucrose and 0.05 mg/ml of urea. We observe two periods in the culture: in the first, Entodinium grows essentially, in the second the population of holotrich ciliates increases. If survival is almost the same, the population is most important in culture with sucrose urea than with sucrose.
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The problem of reducing the sugar content of sugary foods is presented from the food manufacturer's point of view. The distinction is made between the need for artificial sweeteners and the more pressing need for bulking agents with at least some of the technological properties of sugar. In view of the considerable sales success of sugarless confections, accounting for over an estimated 30,000,000 lbs. of sorbitol per annum, the clouded prospect for more general sugar substitution in other food categories is discussed with especial reference to the consequent problems in product claims and nomenclature, and the enormous expense of proving safety and dental claims. Finally, an overview of the competitive consumer and regulatory pressures is given, with an urgent appeal to the dental profession to take the initiative for guiding the food processor to dentally improved foods.
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A phosphoenolpyruvate-dependent sucrose phosphotransferase system (PTS) has been demonstrated, by an enzyme-coupled reaction and product isolation, in decryptified cell suspensions of the cariogenic microorganism Streptococcus mutans NCTC 10449. The apparent sucrose PTS reaction for sucrose-adapted, sucrose-challenged cells displayed saturation kinetics with an apparent Km of 7.14 x 10(-5) M, which was distinct from the Km of the glucose PTS activity of glucose-adapted, glucose-challenged cells. Both the sucrose and the glucose PTS activities appear to be inducible and under separate genetic control. The sucrose PTS reaction demonstrated in decryptified cells had an absolute requirement for phosphoenolpyruvate. Only 2-phosphoglycerate, the immediate glycolytic precursor of phosphoenolpyruvate, was found to substitute for phosphoenolpyruvate in this reaction in the absence of fluoride. The sucrose PTS activity of sucrose-adapted cells was competitively inhibited by raffinose and lactose; these same sugars had no effect on the apparent glucose PTS activity. Fructose was the only carbohydrate tested other than sucrose which elicited an apparent PTS reaction in sucrose-adapted cells. The product of the sucrose PTS reaction was isolated and behaved chromatographically on a Dowex-1-X8 column like a monophosphate ester. Alkaline phosphatase treatment of the presumptive sucrose monophosphate liberated a component which behaved chromatographically like free sucrose. Subsequent acid hydrolysis of this component produced moieties which behaved chromatographically like glucose and fructose.
Sucrose catabolism by Streptococcus mutans is initiated by a phosphoenolpyruvate-dependent sucrose phosphotransferase reaction that produces sucrose 6-phosphate the latter is then cleaved by a sucrose 6-phosphate hydrolase reaction that yields glucose 6-phosphate and fructose. We have examined the regulation of the sucrose 6-phosphate hydrolase and found that it was synthesized constitutively whereas sucrose phosphotransferase activity was inducible. However, the levels of both sucrose phosphotransferase and sucrose 6-phosphate hydrolase were repressed when fructose was used as a growth substrate. The specific activity of sucrose 6-phosphate hydrolase in permeabilized cells was approximately 30 mmol/min per mg (dry weight of cells), and it had an apparent Km for sucrose 6-phosphate of 0.3 mM. analysis of a mutant that was missing sucrose 6-phosphate hydrolase activity revealed that its ability to hydrolyze sucrose was reduced.
1. The effect of overloading of hamster fibroblast lysosomes with sucrose on the turnover of lysosomal and Golgi-apparatus enzymes was studied. Arylsulphatase B and UDP-galactose-N-acetylglucosamine galactosyltransferase were chosen as appropriate marker enzymes. The relative contributions of changes in the rates of synthesis and degradation to the increased activities of these enzymes after uptake of sucrose were examined by isotopic-labelling experiments. The effects of sucrose uptake on the degradation of total cellular protein and of the cytoplasmic enzyme, alkaline ribonuclease, were determined for comparative purposes. 2. The rates of enzyme synthesis in the presence and absence of sucrose were compared by pulse-labelling the cells with 14C-labelled amino acids, followed by isolation of purified enzymes and determination of their radioactivity. Sucrose uptake produced increases of 270% and 90% respectively in the rates of synthesis of arylsulphatase B and galactosyltransferase, whereas the rate of synthesis of alkaline ribonuclease was not affected. 3. The rates of degration of the enzymes were estimated by measuring the decay with time of the radioactivity of purified enzymes from prelabelled cells. In the absence of sucrose, the apparent half-lives of arylsulphatase B and galactosyltransferase were about 30 days and 40h respectively. After uptake of sucrose, the half-life of arylsulphatase B decreased to about 10 days and that of galactosyltransferase to 10h. Neither the half-life of alkaline ribonuclease (4 days) nor the rate of degradation of total cellular protein was affected by the uptake of sucrose. 4. These results indicate that the hyperactivity of lysosmal and Golgi-apparatus enzymes after the uptake of sucrose is accompanied by increases in the rates of both synthesis and degradation, and that the increased rates of degradation are insufficient to prevent accumulation of the excess of enzymes synthesized; also that the effects of sucrose uptake are restricted to the vacuolar apparatus.
1. The absorption of glucose and fructose derived from sucrose has been studied using in vitro and in vivo loops of the rat jejunum.2. At low sucrose concentrations (1 and 10 mM) glucose appeared in the serosal compartment of the in vitro preparation at a faster rate than fructose, but at high sucrose concentrations (50 and 100 mM) the rates of serosal transfer of the two sugars were similar. Glucose and fructose appeared in the mucosal compartment, with the rate of fructose appearance exceeding that of glucose, at all the sucrose concentrations studied.3. Phlorizin (5 x 10(-5)M) added to the mucosal medium of the in vitro preparation abolished the serosal transfer of glucose derived from 50 mM sucrose, and reduced that of fructose by 75%.4. In the absence of sodium ions, the in vitro preparation failed to transfer glucose and fructose derived from 50 mM sucrose, into the serosal compartment.5. Glucose was actively accumulated in the whole gut wall of the in vivo preparation to concentrations higher than those in the plasma at 50 and 100 mM, but not at 10 mM sucrose concentrations. Fructose was also actively accumulated to about half the extent of glucose, but reached tissue concentrations greater than those in the plasma, at each sucrose concentration.6. The whole wall concentrations of glucose and fructose derived from sucrose added to the lumen continued to rise when the blood supply to the in vivo preparation was terminated.7. No increase in the in vivo whole wall concentrations of glucose and fructose were detected when sucrose was added to the lumen together with concentrations of glucose sufficient to saturate the monosaccharide transport systems.8. The results favour the view that disaccharide hydrolysis and resulting hexose transfer are sequential, separate events.
In the presence of sucrose, Streptococcus mutans grows in large glucan-containing aggregates. Because of reports of linear rather than exponential growth of sucrose-grown cultures, the kinetics of growth of sucrose-grown cultures of S. mutans strain OMZ-176 were compared with those of glucose-grown cultures. Culture turbidity measurements indicated that growth of sucrose cultures was slower, did not follow exponential kinetics, and slowed and stopped at lower absorbance values than did glucose-grown cultures. However, measurements of the rates of accumulation of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein using fully equilibrated radioactively labeled precursors of each of these macromolecular species in sucrose and glucose-grown cultures showed that: (i) for glucose cultures the synthesis of each of the three informational molecules occurred at the same exponential rate, which was identical to the rate of turbidity increase; (ii) for sucrose cultures each macromolecular species was synthesized at the same exponential rate and these rates were identical to the rate of increase of turbidity of the glucose-grown culture for periods of up to 7 h. Furthermore, the ratios of DNA to RNA, RNA to protein, and protein to DNA for the sucrose cultures were identical to those for the glucose cultures for up to 10 doublings. From these data it was concluded that in the presence of sucrose S. mutans grows in a balanced fashion at the same exponential rate as it does in glucose. The deviation from an exponential growth model of the absorbance in sucrose cultures was attributed to an optical artifact due to the formation of large glucan-containing aggregates of cells. The addition of dextranase to sucrose cultures resulted in cultures which increased in turbidity at the same exponential rate as glucose-grown cultures, without affecting the rate or extent of macromolecular synthesis.
The role of sucrose in the colonization of S mutans strain 6715 in conventional Sprague-Dawley rats was studied. A diet with 56% sucrose favored the oral colonization of the test strain compared to diets with 56% glucose or fructose or to laboratory chow as determined by recoveries from extracted teeth ground in tissue grinders. S mutans strain 6715 cells became well established in all rats fed a high sucrose diet with cell inoculums ranging from 10(8) to the lowest effective dose of 10(5) CFU once orally administered; in rats on nonsucrose diets, inoculation with even the highest dose only infrequently resulted in the establishment of S mutans strain 6715. Sucrose- and glucose- grown cells appeared to behave similarly. Colonization of S mutans strain 6715 occurred in all rats fed diets with a sucrose content ranging from 56 to as low as 1%. The establishment of S mutans strain 6715 on the teeth of rats fed diets with a sucrose concentration of 0.1 or 0.01% was impaired and comparable to the diet containing 56% glucose. In rats fed a high glucose diet, uniform establishment and persistence of the test strain occurred after frequent inoculations with about 5 X 10(8) CFU. The colonization under these conditions appeared to be independent of the intestinal canal as a bacterial cell source. These data suggest the possibility that S mutans can establish itself in the human mouth in the absence of dietary sucrose. In rats fed a high glucose diet and inoculated with 10(7) CFU or less, the cells gradually disappeared from the teeth; in contrast, the test strain implanted well in rats fed the sucrose favors firmer attachment of initially weakly attached cells via in situ new glucan synthesis. S mutans strain 6715 also appeared to have some affinity for teeth in the absence of dietary sucrose that may be of ecological significance. Once firmly established in rats fed a high sucrose diet, S mutans strain 6715 maintained itself in high numbers on the teeth after a switch to a high glucose diet during a 14-week period.