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A wide diversity of biological molecules are modified by the addition of sugar residues, and a large number of glycosyltransferases have been identified that are responsible for these reactions. Despite catalyzing closely related reactions, many of these transferases show little apparent sequence homology. By comparing two apparently unrelated families of yeast Golgi mannosyltransferases a short motif containing two aspartate residues was observed that was conserved in both groups of proteins. Mutagenesis of one of the members of these families, the alpha-1,3-mannosyltransferase Mnn1p, showed that altering either of these aspartates eliminates all enzymatic activity. These changes do not appear to affect the overall folding and assembly of Mnn1p. A similar aspartate-containing sequence was found to be conserved in a diverse range of other glycosyltransferase families, much more frequently than would be expected by chance, suggesting that it is a feature of the catalytic site, or an element of a structural fold, shared by many glycosyltransferases

Resistance to organophosphorus (OP) insecticides is associated with decreased carboxylesterase activity in several insect species. It has been proposed that the resistance may be the result of a mutation in a carboxylesterase that simultaneously reduces its carboxylesterase activity and confers an OP hydrolase activity (the \"mutant aliesterase hypothesis\"). In the sheep blowfly, Lucilia cuprina, the association is due to a change in a specific esterase isozyme, E3, which, in resistant flies, has a null phenotype on gels stained using standard carboxylesterase substrates. Here we show that an OP-resistant allele of the gene that encodes E3 differs at five amino acid replacement sites from a previously described OP-susceptible allele. Knowledge of the structure of a related enzyme (acetylcholinesterase) suggests that one of these substitutions (Gly 137 replaced by Asp) lies within the active site of the enzyme. The occurrence of this substitution is completely correlated with resistance across 15 isogenic strains. In vitro expression of two natural and two synthetic chimeric alleles shows that the Asp 137 substitution alone is responsible for both the loss of E3's carboxylesterase activity and the acquisition of a novel OP hydrolase activity. Modeling of Asp137 in the homologous position in acetylcholinesterase suggests that Asp 137 may act as a base to orientate a water molecule in the appropriate position for hydrolysis of the phosphorylated enzyme intermediate

Recent studies of nitrogen (N) cycling in arctic tundra have indicated that inorganic N supplied to plants by mineralization is not sufficient to meet the annual requirement of N by many tundra species. Whereas N mineralization is slow in tundra soils and concentrations of inorganic N are low, these soils have large stocks of both structural and soluble organic N. In light of these observations, kinetics of absorption of three amino acids (glycine, aspartic acid, and glutamic acid) were measured in dominant vascular plant species of the four major ecosystems types in arctic Alaska and compared with concentrations of free amino acids in soils. Absorption rates were measured on roots using ^1^4C-labeled substrates. Concentrations of free amino acids in soil were measured on water-extracted samples by high pressure liquid chromatography. All species had higher capacity (V\"m\"a\"x) for ammonium uptake (measured using methylamine as an ammonium analogue) than for any amino acid. However, at concentrations observed in the field, uptake rates estimated for amino acids were similar to (glycine) or less than (aspartic and glutamic acids) that for ammonium. On the basis of these comparisons, uptake rates of the three amino acids together may account for between 10 and 82% of the total N uptake in the field, depending on species and community. Deciduous shrubs had higher uptake rates than the more slowly growing evergreen shrubs, suggesting that new growth created a sink that strongly influenced capacity for amino acid uptake. In general, ectomycorrhizal species had higher amino acid uptake than did non-mycorrhizal species. In species that were sampled from more than one community, amino acid uptake rates were highest in the community where a given amino acid was most abundant in the soil. The results indicate that, in arctic tundra, plants short-circuit the mineralization step of decomposition by directly absorbing amino acids. This implies that in the organic soils of these tundra systems (1) inorganic nitrogen is an inadequate measure of plant-available soil nitrogen, (2) mineralization rates underestimate nitrogen supply rates to plants, (3) the large differences among species in capacities to absorb different forms of N provide ample basis for niche differentiation of what was previously considered a single resource, and (4) by short-circuiting N mineralization, plants accelerate N turnover and effectively exert greater control over N cycling than has been previously recognized.

The aim of this study was to examine the physicochemical properties and amino acid composition of rabbit meat after the enrichment of rabbit diet with oregano, sage, and Eleutherococcus senticosus extracts, and to make a comparison with the commercial product XTRACT and control samples. The addition of oregano and sage extracts as well as El. senticosus in the rabbit diet positively influenced the physicochemical properties of rabbit meat by increasing its energy value (P less than 0.05 - sage). Supplementing rabbits feed with oregano and sage extracts led to an improvement of the amino acid composition (P less than 0.01). These findings are also supported by the good health state of rabbits. The diet enriched with the plant extracts is beneficial for the health state of rabbits and the nutritional quality of rabbit meat.

Eight barrows (Yorkshire x [Finnish Landrace x Dutch Landrace]), initially 30 kg BW, were fitted with ileal cannulas to evaluate the effects of supplementing Ca benzoate (2.4%) and organic acids (OA) in the amount of 300 mEq acid/kg feed on dietary buffering capacity (BC), apparent digestibility and retention of nutrients, and manure characteristics. Swine were allotted in a 2 x 4 factorial arrangement of treatments according to a cyclic (8 x 5) changeover design. Two tapioca-corn-soybean meal-based diets were formulated without and with acidogenic Ca benzoate. Each diet was fed in combination with OA (none, formic, fumaric, or n-butyric acid). Daily rations were equal to 2.8 x maintenance requirement (418 kJ ME/BW(.75)) and were given in two portions. Chromic oxide (.25 g/kg) was used as a marker. On average, Ca benzoate lowered BC by 54 mEq/kg feed. This salt enhanced (P < .05) the ileal digestibility (ID) of DM, OM, arginine, isoleucine, leucine, phenylalanine, alanine, aspartic acid, and tyrosine (by up to 2.4 percentage units). Also, the total tract digestibility (TD) of DM, ash, Ca and GE, and Ca retention (percentage of intake) was greater (P < .05) in swine fed Ca benzoate, whereas N retention remained unaffected. Addition of all OA (formic and n-butyric acid, in particular) exerted a positive effect (P < .05) on the ID of amino acids (except for arginine, methionine, and cysteine). A similar effect (P < .05) was found for the TD of DM, OM, CP, Ca and total P and for the retention of N and Ca. In swine fed Ca benzoate, urinary pH decreased by 1.6 units (P < .001). In conclusion, dietary OA have a beneficial effect on the apparent ileal/total tract nutrient digestibilities, and Ca benzoate increased urine acidity, which could be effective against a rapid ammonia emission from manure of swine.

Changes in amino acid composition of alfalfa (Medicago sativa L.) phloem sap were studied in response to a water deficit. Sap was collected by stylectomy. As the leaf water potential decreased from -0.4 to -2.0 MPa, there was a significant increase of the total amino acid concentration, due to that of some amino acids: proline, valine, isoleucine, leucine, glutamic acid, aspartic acid, and threonine. Asparagine concentration, which is the main amino acid assayed in the phloem sap of alfalfa (it accounts for 70% of the total content), did not vary with the plant water status. The other amino acid concentrations remained stable as leaf water potential varied; in particular, gamma-amino butyric acid concentration remained unchanged, whereas it varied in response to wounding. The more striking change in the sieve tubes was the accumulation of proline which was observed below a leaf water potential threshold value of about -0.9 MPa (concentration x60 for a decrease of leaf water potential from -0.9 to -2.0 MPa). The role of such changes in phloem sap amino acid concentration in osmotic adjustment of growing tissues is discussed

The His to Asp phosphotransfer signal transduction mechanism involves three common signaling domains: the transmitter (or His-kinase), the receiver, and the histidine-containing phototransfer (HPt) domain. Typically, a sensor kinase has a His-kinase domain and a response regulator has a receiver domain containing a phosphoaccepting aspartate, whereas a histidine-containing phototransfer domain serves as a mediator of the histidine-to-aspartate phosphotransfer. This signal transduction mechanism was thought to be restricted to prokaryotes. However, many examples have been discovered in diverse eukaryotic species including higher plants. In Arabidopsis, three sensor kinases have been characterized, namely, ETR1, ERS, and CKI1, which were suggested to be involved in ethylene- and cytokinin-dependent signal transduction pathways, respectively. To date, no response regulator has been discovered in higher plants. We identify five distinct Arabidopsis response regulator genes, each encoding a protein containing a receiver-like domain. In vivo and in vitro evidence that ARRs can function as phosphoaccepting response regulators was obtained by employing the Escherichia coli His-Asp phosphotransfer signaling system.

The objective of this study was to find the interplay between asparagine and carbohydrate profiles of the selected flours and their blends and acrylamide concentrations in the cookies derived from them. Shortcrust cookies were prepared from five different flours such as wheat Poznan flour and flours from spelt-wheat, rice, chickpea, and Amaranth seeds. The rice, chickpea, and amaranth flours were mixed with the wheat Poznan flour in the proportions of 1:1 (w/w), 1:1 (w/w), and 1:3 (w/w), respectively. The cookies were baked at a temperature of 180 deg C for 10 minutes. Cookies obtained from the blend of wheat and chickpea flours (1:1, w/w) contained much less acrylamide (5.7 microg/kg) than those derived from the wheat Poznan flour (41.9 microg/kg). The concentrations of reducing sugars and sucrose in the mixture of wheat and chickpea flours were relatively low in comparison with wheat flour. Consequently, the decrease in the concentrations of carbohydrates, which are acrylamide precursors, was the smallest.

High performance liquid chromatography (HPLC) method with the pre-column derivatisation by AccQ.Tag agent and following determination of these derivates after their separation in reverse phase column followed by fluorescent detection was used for the determination of amino acids in cheeses. The contents of sixteen free amino acids in twenty five cheeses commercially available in the Czech Republic were measured. The total content of free amino acids in the studied cheeses varied in the range from 27 g/kg to 160 g/kg. Among individual amino acids, seven amino acids were more concentrated in all cheese samples and came from three distinctive taste groups: bitter tasting amino acids (leucine, lysine, and phenylalanine), bitter sweet amino acids (proline and valine), and salty-umami amino acids (glutamic acid and aspartic acid). The differences in the contents of the total and individual free amino acids were influenced by the kind of cheese and mainly by the duration and intensity of proteolysis.