SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Three new photoreactive sugar analogues bearing an azido, a diazonium salt or a diazirine group as the photophore as well as a tritium atom were developed. Two of these new photoactivatable compounds gave excellent preliminary results, with a high affinity for the melibiose permease of Escherichia coli.
A glucuronide conjugate of the potent 2-azetidinone cholesterol absorption inhibitor Sch 58235 was synthesized to confirm the structure of a metabolite isolated from in vivo sources. A series of 2-azetidinone glycosides was prepared via Schmidt trichloroimidate methodology. Enhanced cholesterol absorption inhibition was achieved by modification of the sugar moiety.
Solvent-free per-O-acetylation of sugars with stoichiometric acetic anhydride and catalytic iodine proceeds in high yield (90-99%) to give exclusively pyranose products as anomeric mixtures. Without workup, subsequent anomeric substitution employing iodine in the presence of hexamethyldisilane (i.e., TMS-I generated in situ) gives the corresponding glycosyl iodides in 75-95% isolated yield. Alternatively, and without workup, further treatment with dimethyl disulfide or thiol (ethanethiol or thiocresol) gives anomerically pure thioglycosides in more than 75% overall yield.
[reaction: see text] Representative simple or polyhydroxylated, pyrrolidine (e.g, DRAM) or piperidine (e.g., DNJ) imines not only are potential carbohydrate-processing enzyme inhibitors that may be formed as regioisomeric variants but also are scaffolds that may be rapidly elaborated to diversely functionalized aza-sugars through highly diastereoselective organometallic additions.
[chemical reaction: see text]. A simple and efficient method for rearranging 2,3-anhydro carbohydrates to unsaturated sugars has been developed. The exceptionally mild reaction conditions and high stereoselectivity should make this an attractive method for the preparation of unsaturated carbohydrate derivatives.
1. Radioactive products in detached leaf segments were examined after periods of steady-state photosynthesis in (14)CO(2). 2. After exposure to (14)CO(2) for approx. 1sec. more than 93% of the fixed radioactivity was located in malate, aspartate and oxaloacetate. After longer periods large proportions of the radioactivity appeared in 3-phosphoglycerate, hexose monophosphates and sucrose. Similar results were obtained with leaves still attached to the plant. 3. Radioactivity appeared first in C-4 of the dicarboxylic acids and C-1 of 3-phosphoglycerate. The labelling pattern in hexoses was consistent with their formation from 3-phosphoglycerate. 4. The reaction giving rise to C(4) dicarboxylic acid appears to be the only quantitatively significant carboxylation reaction. 5. Evidence is provided that the radioactivity incorporated into the C(4) dicarboxylic acid pool is transferred to sugars via 3-phosphoglycerate. A scheme is proposed to account for these observations.
1. Carbon dioxide fixation by isolated pea chloroplasts was stimulated by the addition of intermediates of the Calvin photosynthesis cycle and by some related compounds. 2. Ribose 5-phosphate and fructose 1,6-diphosphate consistently produced the largest effects; free sugars such as erythrose and sedoheptulose and acids such as glycollate and glyoxylate were largely ineffective or even inhibitory. 3. Small effects were produced by fructose and ribose but not by their isomers, glucose and xylose. 4. Maximal rates in the presence of ribose 5-phosphate varied between 10 and 50mumoles of carbon dioxide fixed/mg. of chlorophyll/hr.
1. A series of d-galactose derivatives substituted at C-1 and C-6 were tested for active accumulation by everted segments of hamster and rat intestine. 2. d-Galactose and 6-deoxy-6-fluoro-d-galactose were accumulated far more rapidly than 6-deoxy- and 6-chloro-6-deoxy-d-galactose, and this is interpreted as due to hydrogen-bonding at C-6 during the transport process. 3. 6-Bromo-6-deoxy- and 6-deoxy-6-iodo-d-galactose were not actively transported, indicating that the allowed size of substituent at C-6 lies between that of chlorine and bromine atoms. 4. Similar results were obtained at C-1. Both methyl alpha-d-galactopyranoside and methyl beta-d-galactopyranoside were well transported, but methyl beta-d-thiogalactopyranoside and 1-deoxy-d-galactose were not transported; d-galactopyranosyl fluoride was transported, but only poorly. Again hydrogen-bonding is suggested. 5. It is proposed that d-glucose is the ideal structure for active transport and that binding occurs at C-1, C-2, C-3, C-4 and C-6. Loss of two or more of these bonds usually causes loss of active transport. 6. By plotting Lineweaver-Burk plots of the rates of transport of the galactose derivatives, the apparent V and K(m) values were obtained. With hamster intestine both these values were very reproducible. Contrary to expectation, V varied for different sugars. 7. The K(i) of some of the analogues modified at C-1 and C-6 was determined with methyl alpha-d-glucoside as substrate. 8. An attempt to alkylate the carrier by using methyl 3,4-anhydro-alpha-d-galactoside was unsuccessful. There was no evidence that this compound was bound to the carrier.
Consistent information on the non-milk extrinsic sugars (NMES) content of foods and the NMES intake by the population is required in order to allow comparisons between dietary surveys. A critical appraisal of methods of NMES estimation was conducted to investigate whether the different published methods for estimating the NMES content of foods lead to significantly different values for the dietary intake of NMES by children and to consider the relative practicality of each method. NMES values of foods were calculated using three different published descriptions of methods of NMES estimation, and the values were compared within food groups. Dietary intake values for English children aged 11-12 years were calculated using each method and compared in terms of overall NMES intake and the contribution of different food groups to NMES intake. There was no significant difference in the dietary intake of NMES in children between the method used in the National Diet and Nutrition Surveys (NDNS) (81.9 g/d; 95 % CI 79.0, 84.7) and a method developed by the Human Nutrition Research Centre (84.3 g/d; 95 % CI 81.4, 87.2) at Newcastle University, UK, although the latter gave slightly higher values. An earlier method used by the Ministry of Agriculture, Food and Fisheries gave significantly higher values than the other two methods (102.5 g/d; 95 % CI 99.3, 105.6; P<0.05). The method used in the NDNS surveys and the method used by the Human Nutrition Research Centre at Newcastle University are both thorough and detailed methods that give consistent results. However, the method used in the NDNS surveys was more straightforward to apply in practice and is the best method for a single uniform approach to the estimation of NMES.
Sugar-lectin binding assay was developed as a simple method which employed direct coating of microtiter plate with galactose-binding lectins. Biotin-galactose conjugate was used to bind to the immobilized lectins. The bound conjugate was then detected using streptavidin-horseradish peroxidase. Using the assay in conjunction with various competing carbohydrates, jackfruit lectin from Artocarpus heterophyllus was found to be specific for alpha-anomer of galactoside with an aromatic residue.
Rations with dried feedstuffs and rations with between 30 and 50% raw potatoes in the dry matter as well as steamed potatoes and sugar beets, sucrose and apple pectin were tested in measurings of the total metabolism in growing pigs with ileo-rectal anastomoses. The prececal digestibility of the energy of the rations ranged between 42% (rations with raw potatoes) and 79% (rations with sucrose). The digestibility of the rations with a 50% quota of steamed potatoes was better by 30%--units than that of rations with raw potatoes. In addition to crude nutrient digestibility, data are given on the digestibility of starch, water soluble carbohydrates and pectin. The wide variation in the N retention of 6-25 g/animal.day can only be partly connected with energy retention. Urine energy amounted to between 2.5 and 5% of gross energy. The average utilization of metabolizable energy amounted to 69.4%. A connection is to be seen with the value of energy maintenance requirement of 646 kJ retention energy/kg LW0.62.d.
Results of the measuring of the total metabolism of growing intact pigs (INT) and pigs with ileorectal anastomoses (IRA) are compared. The 16 comparisons are based on studies with rations of dried feedstuffs and rations containing between 30 and 50% of the DM raw or steamed potatoes and sugar beets, sucrose and apple pectin. On an average of all comparisons the relative values for the digestibility of energy, DM and the organic matter as well as for the metabolizability of the energy were between 81 and 82% (values measured at INT animals = 100). The comparison also refers to the crude nutrients, the water-soluble carbohydrates, the starch and the pectin. As a tendency, the IRA utilized the metabolizable energy better than the INT animals. The energy maintenance requirement of the IRA animals was--by 15%--significantly higher than that of the INT animals. There is not yet an answer to the question in how far comparative studies of INT and IRA animals make verified statements with regard to the differences in the energetic utilization of the precaecally and postileally digested nutrients possible. For this, further experiments will be necessary.
During sucrose uptake by the cotyledons of castor bean seedlings excised from their endosperms, small amounts of glucose and fructose accumulate in the medium. When these hexoses were supplied separately, it was found that the rate of fructose uptake exceeded that of glucose at concentrations up to 0.5 m. Sucrose uptake exceeded that of both hexoses combined, particularly at concentrations greater than 0.1 m. Only minute amounts of labeled hexoses were recovered from the cotyledons after exposure to glucose-U-(14)C or fructose-U-(14)C; sucrose contained virtually all of the (14)C in the sugar fraction. The fructose and glucose moieties of the extracted sucrose were equally labeled when glucose-U-(14)C was supplied, and the glucose moiety contained 41% of the (14)C when fructose-U-(14)C was the substrate.Several considerations led to the conclusion that by far the greater part of sucrose absorbed by the cotyledons was not hydrolyzed prior to or during uptake. These included the differential responses of hydrolysis and uptake to pH, and to Tris(hydroxymethyl) aminomethane, the absence of interference of the hexoses on sucrose absorption and particularly the demonstration that when the cotyledons were supplied with fructosyl-(14)C sucrose, 90% of the (14)C was retained in the fructose residue of sucrose in the cotyledons.
The aetiology of dental caries is in part related to the retention time of dietary carbohydrates in the oral cavity and their subsequent metabolism by the oral bacteria. Salivary clearance of fermentable carbohydrates from three different foodstuffs was examined in 5 subjects and analyses performed by high-performance anion-exchange chromatography with pulsed amperometric detection. The clearance of glucose, fructose, sucrose, maltose and sorbitol rinses was studied as well as that of chocolate bars, white bread and bananas. Of the sugar rinses studied, sucrose was removed from saliva most rapidly whilst appreciable levels of sorbitol remained even after 1 h. Clearance of residual carbohydrates from bananas and chocolate bars seemed marginally faster than in the case of bread, but sucrose levels still tended to fall more quickly than other carbohydrates studied. Surprisingly, carbohydrate residues from the three foods studied were still present in the mouth even 1 h after ingestion, which is longer than has hitherto been reported.
Previously we showed that glycation-induced inactivation and loss of antigenicity of enzymes occur simultaneously. Alpha-crystallin, a major structural protein of the mammalian lens, prevents the aggregation of other proteins and protects enzyme function against post-translational modification in vitro. However, it is not known whether alpha-crystallin can also protect against loss of antigenicity of enzymes. Esterase activity in the lens is decreased in senile cataract and diabetes. We investigated the loss of antigenicity of esterase caused by different insults and the ability of alpha-crystallin to protect. Inactivation of carboxylesterase by sugars, fructose 6-phosphate (F6P) and a steroid, prednisolone-21-hemisuccinate (P-21-H), was measured spectrophotometrically in the presence and absence of alpha-crystallin, while loss of antigenicity was monitored simultaneously using an immunoprecipitation method. The esterase was progressively inactivated by fructose, F6P, ribose, and P-21-H. Bovine alpha-crystallin fully protected against inactivation of esterase by all four compounds, and also protected against loss of antigenicity of the esterase by fructose, ribose and P-21-H at a molar ratio of 1:1. The results indicated that alpha-crystallin, under our experimental conditions, clearly exhibited the ability to prevent loss of antigenicity and inactivation of esterase. The protective effect of alpha-crystallin against loss of antigenicity indicates a novel aspect of its chaperoning function.
The transfer of N-acetyl-D-glucosamine (GlcNAc), D-mannose (Man), D-galactose (Gal) and L-fucose (Fuc) from their nucleotide complexes to isolated rod outer segment (ROS) membranes obtained from dark-adapted 21 +/- 2 days old dystrophic (RCS) and control (RCS-rdy+) rat retinas, was studied under light or dark conditions of incubation. It was found that all of these sugars were transferred to ROS membranes in the dark. Under these conditions there was significantly less (p less than 0.001) Gal transferred to dystrophic than to control membranes. Exposure to light affected the transfer of Gal and Fuc only. Thus, the transfer of Gal and Fuc to control ROS membranes was increased by about 50% compared to the level observed under dark conditions of incubation. On the other hand, exposure to light had no effect on the transfer of Gal to dystrophic ROS membranes but it enhanced the transfer of Fuc to these membranes by about 250% above the level observed in the dark. Under light there were highly significant (p less than 0.001) differences between control and dystrophic membranes in the transfer of Gal and Fuc. The transfer of Fuc to dystrophic ROS membranes was proportional to the concentration of GDP-Fuc but the acceptors on control membranes were saturated at low concentrations of substrate. However, the transfer of Gal from UDP-Gal to both types of membranes was proportional to the concentrations of substrate and ROS membrane protein and to the period of incubation. The transfer of Gal and Fuc to both types of membranes was significantly reduced after denaturation of ROS membrane proteins.(ABSTRACT TRUNCATED AT 250 WORDS)
With use of a specially designed gradient-generating system, of anion-exchange resins of 10-20 mum particle diameter, and of an orcinol solution in concentrated sulfuric acid (1 g/liter) as detection reagent, a mixture of 16 carbohydrates can be separated in less than 4 h. The limit of detection for most sugars is in the 0.1--2.0 nanomole range. The detection reagent is stable for months and does not become colored. The reagent mixes with the column effluent in an exothermic reaction and allows use of relatively short mixing coils. The analyzer is appropriate for investigating body fluids rapidly and with high sensitivity.
This paper critically synthesises available research that examines young people's relationships with sugar daddies and mummies. It considers definitional, measurement and analytical issues involved in assessing these relationships, their magnitude, patterns, determinants and consequences. The review compares and contrasts the experiences of young people in a variety of settings in developing countries versus developed countries, and identifies key associated factors perpetuating those relationships. The implications of this endeavour for data needs and future research and intervention studies targeted at promoting young people's health and well being are discussed within the contexts of globalisation and localisation and recommendations for dealing with these experiences.