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C Seki

Publications and source records attributed to C Seki.

27 records · Page 2Linked to original sources
PubMed1985

Dissociation of the crotoxin complex promoted by acetylcholine.

Neuromuscular blockage at the presynaptic level is the main biological effect exerted by crotoxin, the major toxin from Crotalus durissus terrificus venom. This effect requires the dissociation of this complex at the target membrane in spite of its tightness and stability under physiological conditions of pH, ionic composition and temperature. Complex dissociation should be determined by a specific set of physicochemical conditions prevailing at the neuromuscular junction. In this regard, we have studied the effect of acetylcholine on the stability of the crotoxin complex, since this effector is present at relatively high concentrations near the presynaptic membrane of the neuromuscular junction. Evidences arising from spectrofluorometric measurements, changes in enzymatic activity and crotoxin B inactivation by b-bromophenacyl bromide indicate that acetylcholine is indeed able to promote complex dissociation at neutral pH values, apparently by titration of 2-3 carboxylate groups in crotoxin A. This effect may, at least in part, contribute in determining the target specificity of this toxin.

Acetylcholine↗
PubMed1983

The mechanism of inhibition of phospholipase activity of crotoxin B by crotoxin A.

In the crotoxin complex isolated from Crotalus durissus terrificus venom, the component A inhibits the phospholipase A2 activity of crotoxin B only when the substrate is in the aggregated form, preventing the interaction of the enzyme with lecithin--water interfaces. In contrast, with similar rates of hydrolysis of dihexanoyllecithin monomers, the activity of the crotoxin complex is lower than that of crotoxin B when the substrate is aggregated into micelles. Crotoxin B readily hydrolyses dimyristoyllecithin vesicles, the rate being modulated by the physical state of the phospholipid, suggesting that the enzyme is tightly bound to the interface. With the crotoxin complex the rate of vesicle hydrolysis is much slower (about 1/10 that of crotoxin B) and is little affected by the physical state of the lecithin. Direct binding experiments demonstrate that, in contrast to crotoxin B, the crotoxin complex is unable to interact with lecithin--water interfaces. Together with the free accessibility of the enzyme active site in the crotoxin complex, this evidence suggests that a specific area on the enzyme surface, different from the active site and shielded by crotoxin A in the complex, is responsible for the interaction of crotoxin B with lipid--water interfaces.

Crotalid Venoms↗
PubMed1982

Accessibility of the active site of crotoxin B in the crotoxin complex.

Basic phospholipases A and the crotoxin complex isolated from Crotalus durissus terrificus venom exhibited similar initial reaction rates, time course and degree of hydrolysis of synthetic short chain lecithins in the monomeric state. Although monomeric lecithins seem to promote dissociation of crotoxin up to a certain extent, this cannot explain the high activity observed with the complex. The crotoxin complex is able to bind the non-hydrolyzable analog D-diheptanoyllecithin, as demonstrated by equilibrium gel-filtration, with a dissociation constant of 0.12 mM. This value is similar to the dissociation constant of the crotoxin B-D-diheptanoyllecithin complex (about 0.13 mM), estimated from the protection against enzyme inactivation by p-bromophenacyl bromide, which further supports the free accessibility of the substrate to the enzyme active site in the crotoxin complex. The lack of enzyme inactivation when crotoxin is treated with p-bromophenacyl bromide may be interpreted in terms of the specific requirements of the reagent to react with the enzyme rather than protection of the active site. Crotoxin B inhibition by complex formation with crotoxin A, which is not apparent on monomeric substrates, seems not to involve the active site of the enzyme.

Acetophenones↗
PubMed1982

[Resistance of Crotalus durissus terrificus and Bothrops neuwiedii to the neurotoxicity of massive quantities of Crotalid venom].

The antitoxic potency of crude Crotalus durissus terrificus serum against crotalic venom is similar to that of a standard horse anticrotalic serum in protecting mice against 4 LD50, while the potency of Bothrops neuwiedii serum is 20% of the latter. Failure to form precipitin lines in immunodiffusion tests suggests that the antitoxic factors present in the sera from both species are not immunoglobulins. It is, therefore, probable that crotoxin is not neutralized by an antigen-antibody reaction, but rather by formation of inactive complexes with specific serum components. Resistance to the venom is not reciprocal, since specimens of C. d. terrificus die after the injection of similar amounts of B. neuwiedii venom, which are tolerated by the homologous species.

Animals↗
PubMedDate not supplied

Total and isotype humoral responses in cattle vaccinated with foot and mouth disease virus (FMDV) immunogen produced either in bovine tongue tissue or in BHK-21 cell suspension cultures.

The anti-foot and mouth disease virus (FMDV) serum antibody activity of protected and non protected animals immunized with inactivated FMDV originated in either bovine tongue tissue (BTTV vaccines) or BHK-21 cell suspension cultures (BHKV vaccines) was evaluated. The results show that 80-100% of the BTTV immunized and only 40-60% of the BHKV immunized animals with liquid-phase blocking sandwich ELISA (lp ELISA) serum titres of 1.5-1.7 U, were protected against the challenge with any of the four infectious FMDV argentine reference strains. This difference becomes almost marginal among BTTV and BHKV vaccinated animals with a strong anti-FMDV humoral response (i.e. lp ELISA titres > or = 1.95 U). Isotyping of the anti-FMDV response in immunized cattle with low lp ELISA titres revealed that BTTV vaccines were able to induce remarkably higher anti-FMDV IgG1 titres than their BHKV counterparts (i.e. mean titres of 1.95 and 1.35 U. respectively). This difference in specific IgG1 serum levels induced by BTTV and BHKV vaccines seems to be also limited to those animals with low anti-FMDV lp ELISA titres. These results together with the fact that the specific serum IgG1, but not the IgG2, isotype response of 219 vaccinated animals correlates almost linearly with their capacity to pass the challenge, suggests that the superior performance of BTTV vaccines is close related to their ability to raise a stronger anti-FMDV IgG1 response than BHKV vaccines.

Animals↗
PubMedDate not supplied

Scatter, spatial resolution, and quantitative recovery in high resolution SPECT.

The potential use of single photon emission CT (SPECT) for quantification depends on its physical performance characteristics. We investigated the performance of a high resolution four-head brain SPECT scanner (Neuro-Spect; Summit/Hitachi). With an attenuation coefficient of 0.11 cm-1 and the Chang correction method, the calibration factor of the scanner was 515 (cpm/ml)/(microCi/ml) and showed only a minimal but systematic dependence on object size. Without scatter, the resolution was 4.7 mm (full width at half-maximum); in a scatter medium, the resolution was 5.3-10.0 mm with high resolution collimation and 7.7-18.8 mm with general purpose collimation, depending on filtering. A recovery coefficient of close to 100% was measured in the center of spheres with a size of at least 20 mm placed in a cylindrical water-filled phantom. In lesions of this size, scatter was 20%. We conclude from our measurements that the investigated high resolution SPECT offers significant improvements in resolution, scatter, and recovery, which will improve both the quality of brain studies and the measurement of quantitative parameters such as the cortex/white matter ratio.

Brain↗