Synthesis of 2-acrylamidoethylglycosides of 3-O-(beta-D- glucopyranosyluronic acid)-alpha-L-rhamnose and 3-O-(alpha-L- rhamnopyranosyl)-beta-D-glucopyranuronic acid and copolymeric artificial antigens based on them

The synthesis of disaccharide repeating units, D-GlcA-(beta 1----3)-L-Rha (fragment A) and L-Rha-(alpha 1----3)-D-GlcA (fragment B), of the K54-antigenic polysaccharide from uropathogenic Escherichia coli 06:K54:H10 is described. Essential stages of the synthesis of fragment A involved the glycosylation of methyl 2,4-di-O-benzoyl-alpha-L-rhamnopyranoside followed by acetolysis of the methyl bioside obtained and further transformation into 2-(benzyloxycarbonylamino)ethyl glycoside; deprotection and, finally, conversion into 2-(acrylamido)ethyl glycoside. Selective opening of lactone ring in 2-azidoethyl 2,4-di-O-acetyl-beta-D-glucopyranoside-6,3-lactone was used for deprotection of 3-OH group in the synthesis of fragment B. Rhamnosylation of the glucuronic acid derivative thus obtained followed by transformation into 2-(acrylamido)ethyl glycoside and deprotection gave fragment B. Both fragments A and B were converted into artificial antigens of copolymer type.     

Interaction of uridine diphosphate glucose analogs with calf liver uridine diphosphate glucose dehydrogenase. Influence of substituents at C-5 of pyrimidine nucleus.

The interaction of alpha-D-glucopyranosyl pyrophosphates of 5-X-uridines (X = CH3, NH2, CH3O, I, Br, Cl, OH) with uridine diphosphate glucose (UDPGlc) dehydrogenase (EC 1.1.1.22) from calf liver has been studied. All the derivatives investigated were able to serve as substrates for the enzyme. The apparent Michaelis constants for UDPGlc-analogs were dependent both on electronic and steric factors. Increase of substituent negative inductive effect lead to decrease of pKa for ionization of the NH-group in the uracil nucleus and, consequently, to a diminishing of the proportion of the active analog species under the conditions of assay. After correction for the ionization effect, the Km values were found to depend on the van der Waals radius of the substituent. The value of 1.95 A seems to be critical, as the analogs with bulkier substituents at C-5 showed a decreased affinity to the enzyme. The maximal velocity values of the analogs were also dependent on nature of the substituent. Good linear correlation between log V and substituent hydrophobic phi-constant was observed for a number of the analogs, although V values for the nucleotides with X = H, OH or NH2 were higher than would be expected on the basis of the correlation. The significance of the results for understanding of the topography of UDPGlc dehydrogenase active site is discussed.     

Uridine diphosphate 2-deoxyglucose: Chemical synthesis,enzymic oxidation and epimerization

The paper describes chemical synthesis of uridine diphosphate 2-deoxyglucose (UDPdGlc) through reaction of uridine 5′-phosphomorpholidate with 2-deoxy-α-d-glucopyranosyl phosphate. The prepared analog of uridine diphosphate glucose (UDPGlc) served as a substrate for calf liver UDPGlc dehydrogenase (EC 1.1.1.22), the reaction product was identified as nucleotide deoxyhexuronic acid derivative. The apparent K_m for UDPdGlc was found to be 60 times that of UDPGlc, and the relative V value for the analog was 0.09. The peculiar lag-period in reaction kinetics has been observed for the analog, and is presumably connected with the slow rate of the initial stages of the reaction. UDPdGlc was found to be quite an efficient substrate for UDPGlc 4-epimerases (EC 5.1.3.2) from yeast, calf liver and mung bean seedlings.     

Somatic antigens of Shigella. Structural investigation on the O-specific polysaccharide chain of Shigella dysenteriae type-2 lipopolysaccharide.

The O-specific polysaccharide obtained from Shigella dysenteriae type-2 lipopolysaccharide by mild acid hydrolysis consisted of N-acetylgalactosamine, N-acetylglucosamine, D-galactose, D-glucose, and O-acetyl group in the ratio of 2:1:1:1:1. A number of oligosaccharides were obtained by deamination of the N-deacetylated polysaccharide and by Smith degradation of the both native and O-deacetylated polysaccharides. The identification of oligosaccharides along with methylation analysis and chromic anhydride oxidation showed that the polysaccharide was built up of the repeating pentasaccharide units whose proposed structure is given below: (see article) Serological properties of Sh. dysenteriae O-specific polysaccharides are discussed.     

RNA-dependent RNA polymerase of hepatitis C virus: Study on inhibition by α,γ-diketo acid derivatives

It is supposed that α,γ-diketo acids (DKAs) inhibit the activity of hepatitis C virus RNA-dependent RNA poly-merase (RdRP HCV) via chelation of catalytic magnesium ions in the active center of the enzyme. However, DKAs display noncompetitive mode of inhibition with respect to NTP substrate, which contradicts the proposed mechanism. We have examined the NTP substrate entry channel and the active site of RdRP HCV for their possible interaction with DKAs. The substitutions R48A, K51A, and R222A greatly facilitated RdRP inhibition by DKAs and simultaneously increased K _m values for UTP substrate. Interestingly, C223A was the only one of a number of substitutions that decreased K _m(UTP) but facilitated the inhibitory action of DKAs. The findings allowed us to model an enzyme-inhibitor complex. According to the proposed model, DKAs introduce an additional Mg²⁺ ion into the active site of the enzyme at a stage of phosphodiester bond formation, which results in displacement of the NTP substrate triphosphate moiety to a catalytically inactive binding mode. This mechanism, in contrast to the currently adopted one, explains the noncompetitive mode of inhibition.     

Rhizosphere bacteria Pseudomonas aureofaciens and Pseudomonas chlororaphis oxidizing naphthalene in the presence of arsenic

Rhizosphere strains of P. aureofaciens BS1393(pBS216, pKS1) and P. chlororaphis PCL1391(pBS216, pKS1), exhibiting the ability to stimulate the growth of plants and protect them from phytopathogens, have been obtained. In these strains, plasmid pBS216 ensures naphthalene degradation and plasmid pKS1 confers resistance to arsenic. In the presence of arsenic and naphthalene, the number of living cells and the growth rate of the arsenic-resistant strains were higher than those of the arsenic-sensitive strains BS1393(pBS216) and PCL1391(pBS216). During the cultivation of the resistant strains, arsenic had no inhibitory effect on the activity of the key enzymes of naphthalene biodegradation, except for catechol-2,3-dioxygenase. In a model system containing plant-microbial associations, strains BS1393(pBS216, pKS1) and PCL1391(pBS216, pKS1) degraded as much as 97% of added naphthalene in the presence of arsenic.