Neodictyoprolenol and dictyoprolenol, the possible biosynthetic intermediates of dictyopterenes, in the Japanese brown algae Dictyopteris

Neodictyoprolenol [(-)-(3S)-(1,5Z,8Z)-undecatrien-3-ol] and dictyoprolenol [(-)-(3S)-(1,5Z,8Z)-undecadien-3-ol]), which had been proposed as possible biosynthetic intermediates of the sex pheromones of marine brown algae such as dictyopterene B [(-)-trans-1-((1'E,3'Z)-hexadienyl)-2-vinylcyclopropane], D' [(+)-6-((1'Z)-butenyl)-1,4-cycloheptadiene] and C' [(+)-6-butyl-1,4-cycloheptadiene], were again identified in the essential oils from Dictyopteris prolifera, D. latiscula, and in D. undulata, together with the C11-related volatile compounds such as neodictyoprolene, dictyoprolene and dictyopterenes. Incubation of D. prolifela preparation with racemic neodictyoprolenol and dictyoprolenol as substrates showed (S)-enantioselective decreases of the added substrates and increases in dictyopterenes. From these results, a possible pathway to form dictyopterenes is discussed.     

Recombinant Rhodococcus sp. strain T09 can desulfurize DBT in the presence of inorganic sulfate

The putative Rhodococcus rrn promoter region was cloned from the benzothiophene desulfurizing Rhodococcus sp. strain T09, and the dibenzothiophene desulfurizing gene, dsz, was expressed under the control of the putative rrn promoter in the strain T09 using a Rhodococcus–E.coli shuttle vector. Strain T09 harboring the expression vector, pNT, could desulfurize dibenzothiophene in the presence of inorganic sulfate, methionine, or cysteine, while the Dsz phenotype was completely repressed in recombinant cells carrying the gene under the control of the native dsz promoter under the same conditions. Among the sulfur sources examined, no intermediates were detected and only the final desulfurized product, 2-hydroxy-biphenyl, was produced using ammonium sulfate as the sulfur source. Received: 4 December 2001 / Accepted: 7 January 2002     

Association of a regulatory gene, slyA with a mouse virulence of Salmonella serovar Choleraesuis

The influence of slyA gene, originally found in Salmonella serovar Typhimurium as a regulatory gene for the expression of virulence genes, on a mouse virulence of S. serovar Choleraesuis was investigated by using an slyA-defective mutant. The defective mutant was constructed by the insertion of a kanamycin-resistance gene (aph) into the cloned slyA gene, and the homologous recombination with the intact slyA gene on the chromosome. The mutant strain showed the LD50 value for BALB/c mouse approximately 10(5) higher than that of the parent strain. The increase of the LD50 value was the same order as that shown by the mutation of the slyA gene of S. serovar Typhimurium, although LD50 of the wild-type strain of S. serovar Choleraesuis was 40-fold higher than that of S. serovar Typhimurium. The time course of infection observed in the mice organs also proved the clear difference of the virulence between the parent and the mutant strains. These results suggested that the slyA gene product functions as a virulence-associated regulator also in S. serovar Choleraesuis.     

Binding site on human von Willebrand factor of bitiscetin,a snake venom-derived platelet aggregation inducer

Bitiscetin, a C-type lectin-like heterodimeric snake venom protein purified from Bitis arietans, binds to human von Willebrand factor (VWF) and induces the platelet membrane glycoprotein (GP) Ib-dependent platelet agglutination in vitro similar to botrocetin. In contrast with botrocetin which binds to the A1 domain of VWF, the A3 domain, a major collagen-binding site of VWF, was proposed to be a bitiscetin-binding site. In the competitive binding assay, neither bitiscetin nor botrocetin had an inhibitory effect on the VWF binding to the immobilized type III collagen on a plastic plate. The anti-VWF monoclonal antibody NMC-4, which inhibits VWF-induced platelet aggregation by binding to alpha4 helix of the A1 domain, also inhibited bitiscetin binding to the VWF. Binding of VWF to the immobilized bitiscetin was competitively inhibited by a high concentration of botrocetin. A panel of recombinant VWF, in which alanine-scanning mutagenesis was introduced to the charged amino acid residues in the A1 domain, showed that the bitiscetin-binding activity was reduced in mutations at Arg632, Lys660, Glu666, and Lys673 of the A1 domain. Those substituted at Arg629, Arg636, and Lys667, which decreased the botrocetin binding, showed no effect on the bitiscetin binding. These results indicate that bitiscetin binds to a distinct site in the A1 domain of VWF spanning over alpha4a, alpha5 helices and the loop between alpha5 and beta6 but close to the botrocetin- and NMC-4-binding sites. Monoclonal antibodies recognizing the alpha-subunit of bitiscetin specifically inhibited bitiscetin-induced platelet agglutination without affecting the binding between VWF and bitiscetin, suggesting that the alpha-subunit of bitiscetin is located on VWF closer to the GPIb-binding site than the beta-subunit is. Bitiscetin and botrocetin might modulate VWF by binding to the homologous region of the A1 domain to induce a conformational change leading to an increased accessibility to platelet GPIb.     

Disruption of adiponectin causes insulin resistance and neointimal formation

The adipocyte-derived hormone adiponectin has been proposed to play important roles in the regulation of energy homeostasis and insulin sensitivity, and it has been reported to exhibit putative antiatherogenic properties in vitro. In this study we generated adiponectin-deficient mice to directly investigate whether adiponectin has a physiological protective role against diabetes and atherosclerosis in vivo. Heterozygous adiponectin-deficient (adipo(+/-)) mice showed mild insulin resistance, while homozygous adiponectin-deficient (adipo(-/-)) mice showed moderate insulin resistance with glucose intolerance despite body weight gain similar to that of wild-type mice. Moreover, adipo(-/-) mice showed 2-fold more neointimal formation in response to external vascular cuff injury than wild-type mice (p = 0.01). This study provides the first direct evidence that adiponectin plays a protective role against insulin resistance and atherosclerosis in vivo.     

Phosphorylation of neuroglycan C, a brain-specific transmembrane chondroitin sulfate proteoglycan, and its localization in the lipid rafts

Neuroglycan C (NGC) is a brain-specific transmembrane chondroitin sulfate proteoglycan. In the present study, we examined whether NGC could be phosphorylated in neural cells. On metabolic labeling of cultured cerebral cortical cells from the rat fetus with (32)P(i), serine residues in NGC were radiolabeled. Some NGC became detectable in the raft fraction from the rat cerebrum, a signaling microdomain of the plasma membrane, with cerebral development. NGC from the non-raft fraction, not the raft fraction, could be phosphorylated by an in vitro kinase reaction. The phosphorylation of NGC was inhibited by adding to the reaction mixture a recombinant peptide representing the ectodomain of NGC, but not by adding a peptide representing its cytoplasmic domain. NGC could be labeled by an in vitro kinase reaction using [gamma-(32)P]GTP as well as [gamma-(32)P]ATP, and this kinase activity was partially inhibited by 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole, a selective inhibitor of casein kinase II. In addition to the intracellular phosphorylation, NGC was also phosphorylated at the cell surface by an ectoprotein kinase. This is the first report to demonstrate that NGC can be phosphorylated both intracellularly and pericellularly, and our findings suggest that a kinase with a specificity similar to that of casein kinase II is responsible for the NGC ectodomain phosphorylation.     

Changes in mutagenicity of herbicide chlornitrofen during biodegradation

We used the Ames assay to investigate changes in the mutagenicity of chlornitrofen during its aerobic biodegradation. Although a mixed culture of bacteria obtained from river water degraded chlornitrofen and reduced its concentration from 39 to 6 microg/l in 21 days, the indirect mutagenicity of the solution to Salmonella strains TA98, YG1021, and YG1026 increased gradually. This finding suggests that mutagenic metabolites were produced during the aerobic biodegradation. The increase in the mutagenicity was, however, much smaller under aerobic than under anaerobic conditions. The differing sensitivities of our test strains to the functional groups on the mutagens showed that the mutagenic metabolites were indirect frameshift-type mutagens that might have neither nitro nor amino groups.     

Luteolin,a flavone,does not suppress postprandial glucose absorption through an inhibition of alpha-glucosidase action

In order to clarify the postprandial glucose suppression via alpha-glucosidase (AGH) inhibitory action by natural compounds, flavonoids were examined in this study. Among the flavonoids (luteolin, kaempferol, chrysin, and galangin), luteolin showed the potent maltase inhibitory activity with the IC50 of 2.3 mM, while less inhibitions were observed against sucrase. In addition, the effects of maltase inhibition by flavonoids were observed in the descending order of potency of luteolin > kaempferol > chrysin > galangin. Apparently, the AGH inhibition power greatly increased with the replacement of hydroxyl groups at 3' and 4'-position of the B-ring. However, the inhibitory power of luteolin was poorer than a therapeutic drug (acarbose: IC50; 430 nM). As a result of a single oral administration of maltose or sucrose (2 g/kg) in SD rats, no significant change in blood glucose level with the doses of 100 and 200 mg/kg of luteolin was observed. These findings strongly suggested that luteolin given at less than 200 mg/kg did not possess the ability to suppress the glucose production from carbohydrates through the inhibition of AGH action in the gut.     

A hyperthermostable D-ribose-5-phosphate isomerase from Pyrococcus horikoshii characterization and three-dimensional structure

A gene homologous to D-ribose-5-phosphate isomerase (EC 5.3.1.6) was found in the genome of Pyrococcus horikoshii. D-ribose-5-phosphate isomerase (PRI) is of particular metabolic importance since it catalyzes the interconversion between the ribose and ribulose forms involved in the pentose phosphate cycle and in the process of photosynthesis. The gene consisting of 687 bp was overexpressed in Escherichia coli, and the resulting enzyme showed activity at high temperatures with an optimum over 90 degrees C. The crystal structures of the enzyme, free and in complex with D-4-phosphoerythronic acid inhibitor, were determined. PRI is a tetramer in the crystal and in solution, and each monomer has a new fold consisting of two alpha/beta domains. The 3D structures and the characterization of different mutants indicate a direct or indirect catalytic role for the residues E107, D85, and K98.