The stepwise synthesis of methyl α-isomaltooligoside derivatives and methyl α-isomaltopentaoside

Methyl 2,3,4-tri-O-benzyl-α-D-glucopyranoside was treated with 2,3,4-tri-O-benzyl-6-O-(N-phenylcarbamoyl)-1-O-tosyl-D-glucopyranose in diethyl ether to give methyl 2,3,4,2',3',4'-hexa-O-benzyl-6'-O-(N-phenylcarbamoyl)-α-isomaltoside. The disaccharide was decarbanilated in ethanol with sodium ethoxide to give methyl 2,3,4,2',3',4'-hexa-O-benzyl-α-isomaltoside. The sequence of coupling with the same 1-O-tosyl-D-glucose derivative followed by removal of the N-phenylcarbamate group was repeated until the hexasaccharide derivative, methyl octadeca-O-benzyl-α-isomaltohexaoside, was formed. Methyl α-isomaltopentaoside was prepared by debenzylation of the corresponding benzylated oligosaccharide. The structures of the oligosaccharides were determined with the aid of both ¹H- and ¹³C-n.m.r. spectroscopy. From spectral data, we estimate the coupling reaction to be 95% stereoselective.     

Vitamin A in liposomes. Inhibition of complement binding and alteration of membrane structure.

Incorporation of vitamin A aldehyde (retinal) into liposomes had an inhibitory effect on the amount of human complement protein bound in the presence of specific antiserum. The total membrane-bound protein was directly measured on liposomes which were washed after incubation in antiserum and fresh human serum (complement). At every concentration of complement, decreased protein binding was found with liposomes which contained retinal. Binding of the third component of complement (C3) was also measured directly on washed liposomes and was found to be decreased in the presence of retinal. The diminution in protein binding due to retinal was not caused by differences in the amount of antibody bound and this was shown by two experiments. First, specific antibody protein binding to liposomes was directly measured and was essentially unaffected by retinal. Second, liposomes were prepared from lipid extracts of sheep erythrocytes. These liposomes were used as as immunoadsorbants to remove antisheep erythrocyte antibodies. The immunoadsorbant capacity was the same in both the presence and the absence of retinal. A further conclusion from these experiments was that retinal did not change the number of liposomal glycolipid antigen molecules available for antibody binding and thus presumably did not change the total number of lipid molecules present on the outer surface of the liposomes. Retinal did have an effect on the geometric structure of the liposomes. Size distribution measurements were performed in the diameter range of 1-6.35 mum by using an electronic particle size analyzer (Coulter Counter). Liposomes containing retinal were shifted toward smaller sizes and had less total surface area and volume. It was suggested that retinal-containing liposomes may have had a tighter packing of the molecules in the phospholipid bilayer. This effect of retinal on liposomal structure may have been responsible for the observed decreased binding of C3 and total complement protein.     

Kinetics of mucopolysaccharide and glycoprotein synthesis by chick embryo chondrocytes. Effect of D-glucose concentration in the culture medium.

Late log cultures of chick embryo vertebral chondrocytes in Dulbecco's Modified Eagle's Medium with 10% fetal calf serum consume D-glucose from the culture medium at a rate of approximately 0.40 mumol per h per 10(6) cells. When the D-glucose concentration in the medium drops below 1 mumol per ml the glycogen stores are rapidly exhausted, and cell growth ceases. 35SO4(2)- is incorporated into chondroitin-6-SO4 and chondroitin-4-SO4 at linear rates of 1.2 and 0.4 nmol per h per 10(6) cells, respectively, until the D-glucose level in the medium drops below 1 mumol per ml, but there is always a slight lag in the initial appearance of chondroitin-4-SO4. Throughout the period of 35SO4 2- labeling, the amount of chondroitin-6-SO4 that is recovered in the cells exceeds the amount that is recovered in the medium, but the opposite is true for chondroitin-4-SO4. However, when cells prelabeled with 35SO4(2-) are then transferred to a label-free medium, the secretion of chondroitin sulfates proceeds at much slower rates, and the kinetics of chondroitin-6-SO4 and chondroitin-4-SO4 secretion are very similar. In this chase experiment the chondroitin sulfates are recovered quantitatively after a 24-h incubation period, indicating that these embryonic chondrocytes do not degrade the chondroitin sulfates under these culture conditions. The rate of incorporation of counts from D-[14C]glucosamine into mucopolysaccharides and glycoproteins increase with time. This nonlinear rate results from a progressive increase in the specific activity of the UDP-N-acetyl-D-[14C]hexosamine pool as the D-glucose in the culture medium is depleted. A linear relationship is demonstrated between the logarithm of the 14C counts per min per nmol of UDP-N-acetylhexosamine and the logarithm of the concentration of D-glucose in the culture medium over a range of 1 to 20 mumol of D-glucose per ml. The relative rates of appearance of counts from 35SO4(2-) and D-[14]glucosamine in chondroitin 4-SO4 and chondroitin-6-SO4 are used to calculate the specific activity of the UDP-N-acetyl-D-[14C]hexosamine pool at each stage in the labeling period. The resulting values are then used to calculate the rates of synthesis of the nonsulfated polymers, namely, chondroitin, hyaluronic acid, and glycoprotein.     

Effect of oral contraceptives and pregnancy on erythrocyte deformability and surface charge.

Erythrocyte deformability and surface charge were studied in normal premenopausal women, oral contraceptive users, and pregnant women. The increased incidence of thrombosis in women taking oral contraceptives could not be explained by decreased erythrocyte deformability or surface charge. However, the decreased erythrocyte deformability of late pregnancy may relate to thrombosis during this period and to increased hemolysis in patients with certain hemoglobinopathies.     

Environmental history and physiological state influence feeding responses of Atrina zelandica to suspended sediment concentrations

Epifaunal suspension-feeding bivalves can play important roles in marine ecosystems affecting macrobenthic communities, benthic boundary layers and benthic-pelagic coupling, not just by their presence but also by any changes in feeding behaviour. While seston quality and quantity have consistently been found to be important influences on the feeding rates of suspension-feeding bivalves, factors stressing individuals are also likely to be important, as they may affect energy-dependent thresholds of response. We postulated that (1) history of seston quantity would affect how suspension feeders deal with increases in total suspended particulates, and (2) high-seston concentrations would affect feeding rates more in individuals whose energy reserves were low after spawning. Three sites were selected for short-term (1 day) feeding experiments on the pinnid bivalve, Atrina zelandica. At one site, the experiment was run pre-and postspawning. Atrina exhibited high rejection of filtered particles (mostly 75% to 100%) and high organic absorption efficiencies (0.9-1) at all seston levels. Strong differences in the response of feeding behaviour to increased seston concentrations were observed between A. zelandica from the different sites, with lesser differences observed between times. The site-specific feeding responses to seston concentrations observed are likely to affect our ability to model responses of A. zelandica to sediment loading and to influence the importance of A. zelandica to benthic-pelagic coupling.     

Natural selection and the evolution of neutralism

The efficiency of evolutionary search increases as the density of acceptable proteins in a protein space increases. Populations caught in regions whose density is too low to support evolution can be pulled into high density regions by hitchhiking selection. As they move into such regions, the action of natural selection becomes more effective, yet these populations will satisfy conditions which lead to predictions made by neutral, so-called non-Darwinian models.     

Effect of various pre-treatments on the seedling growth performance of Tamarindus indica L.

ABSTRACT

Pre-treatment of seeds of Tamarindus indica L. with 95% sulphuric acid for 5, 10 or 15 min, methanol, ethanol, iso-propanol or butanol for 10 or 20 min, or boiling water for 10, 15, 20 or 30 min, was used to determine the effect of the various treatments on the development and vigour of the resultant seedlings. Seeds immersed in methanol, ethanol and sulphuric acid for 10 min produced seedlings with high vigour     

Microbial production and uptake of nitric oxide in soil

Abstract Fluxes of NO from three different soils have been studied by a flow-through system in the laboratory as a function of gas flow rate, of NO mixing ratio, and of incubation conditions. The dependence of net NO fluxes on gas flow rates and on NO mixing ratios could be described by a simple model of simultaneous NO production and NO uptake. By using this model, rates of gross NO production, rate constants of NO uptake, and NO compensation mixing ratios could be determined as function of the soil type and the incubation condition. Gross NO production rates were one to two orders of magnitude larger under anaerobic than under aerobic conditions. NO uptake rate constants, on the other hand, were only 5–8 times larger so that the compensation mixing ratios of NO were in a range of about 1600–2200 ppbv under anaerobic and of about 50–600 ppbv under aerobic conditions. The different soils exhibited similar NO uptake rate constants, but the gross NO production rate and compensation mixing ratio was significantly higher in an acidic (pH 4.7) sandy clay loam than in other less acidic soils. Experiments with autoclaved soil samples showed that both NO production and NO uptake was mainly due to microbial metabolism.