Role of the N-terminal region of the A chain in beta 1-bungarotoxin from the venom of Bungarus multicinctus (Taiwan-banded krait)

The N-terminal -amino groups of ₁-bungarotoxin (₁-Bgt) fromBungarus multicinctus venom were modified with trinitrobenzene sulfonic acid and the modified derivative was separated by high performance liquid chromatography. The trinitrophenylated (TNP) derivative contained two TNP groups at the -amino groups of A chain and B chain and showed a marked decrease in enzymatic activity. Methionine residues at positions 6 and 8 of the A chain were oxidized with chloramine T or cleaved with cyanogen bromide to remove the N-terminal octapeptide. Oxidation of methionine residues and removal of the N-terminal octapeptide caused a precipitous decrease in enzymatic activity, whereas antigenicity remained unchanged. The presence of dihexanoyllecithin influenced the interaction between ₁-Bgt and 8-antilinonaphthalene sulfonate (ANS) and revealed that ₁-Bgt consists of two types of ANS-binding sites, one at the substrate binding site of the A chain and the other might be at the B chain. The modified derivatives still retained their affinity for Ca²⁺ and ANS, indicating that the N-terminal region is not involved in Ca²⁺ and substrate binding. A fluorescence study revealed that the -amino group of the A chain was in the vicinity of substrate binding site and that the TNP -amino groups were in proximity to Trp-19 of the A chain. In addition, the study showed that the N-terminal region is important for stabilizing the architectural environment of Trp-19. The results, together with the proposal that Trp-19 of the A chain is involved in substrate binding, suggest that the N-terminal region of the A chain plays a crucial role in maintaining a functional active site for ₁-Bgt.     

An in-vivo measurement and analysis of viscoelastic properties of the spinal cord of cats

An in-vivo experimental technique was employed to determine the linear and nonlinear characteristics of viscoelastic properties of the spinal cord of anesthetized cats. The stress relaxation and recovery curves were reproducible in a group of cat experiments. The data of linear viscoelastic properties were used to develop a power law model with Boltzmann's convolution integral. The model was capable of predicting a prolonged stress relaxation and recovery curve. For larger deformation, the results were quantified using a nonlinear analysis of viscoelastic response of the spinal cord under the uniaxial experiment.     

Laboratory investigations of mars: Chemical and spectroscopic characteristics of a suite of clays as Mars Soil Analogs

Two major questions have been raised by prior explorations of Mars. Has there ever been abundant water on Mars? Why is the iron found in the Martian soil not readily seen in the reflectance spectra of the surface? The work reported here describes a model soil system of Mars Soil Analog Materials, MarSAM, with attributes which could help resolve both of these dilemmas. The first set of MarSAM consisted of a suite of variably iron/calcium-exchanged montmorillonite clays. Several properties, including chemical composition, surface-ion composition, water adsorption isotherms, and reflectance spectra, of these clays have been examined. Also, simulations of the Viking Labeled Release Experiment using the MarSAM were performed. The results of these studies show that surface iron and adsorbed water are important determinants of clay behavior as evidenced by changes in reflectance, water absorption, and clay surface reactions. Thus, these materials provide a model soil system which reasonably satisfies the constraints imposed by the Viking analyses and remote spectral observations of the Martian surface, and which offers a sink for significant amounts of water. Finally, our initial results may provide insights into the mechanisms of reactions that occur on clay surfaces as well as a more specific approach to determining the mineralogy of Martian soils.     

Estimation of oxygen penetration depth in immobilized cells

Summary A simple method is proposed for calculating oxygen pentration depth in immobilized cells by assuming zero order kinetics in the presence of several external oxygen transport resistances. Calculations indicate that typical penetration depths of oxygen for immobilized microbial cells are in the range of 50–200 and those for immobilized or encapsulated animal and plant tissue culture are about 500–1000 . Based on calculations, oxygen transport in microencapsulation and microcarriers for tissue cultures are not transport-limited, but a slight limitation is expected for those in a hollow fiber reactor.Nomenclature a_s specific area of a support (cm) - Bi Biot number - dimensionless - C_b oxygen concentration in the bulk liquid (mM) - C _b C _b ^* -C_cr (mM) - C _b ^* bulk oxygen concentration in equilibrium with air (mM) - C_cr critical oxygen concentration (mM) - C_s oxygen concentration in the solid phase (mM) - d_p diameter or thickness of a support (cm) - D_eff effective diffusivity of oxygen in the solid phase (cm²/s) - k_m membrane permeability of oxygen (cm/s) - k _m ^* D_eff/_m - k_La_L liquid phase mass transfer rate coefficient (1/s) - k_sa_s solid phase mass transfer rate coefficient (1/s) - (OUR)_v volumetric oxygen uptake rate (mmol O₂/l) - p geometry parameter, p=0 for slab, p=1 for cylinder, p=2 for sphere - P_d oxygen penetration depth (cm) - P _d oxygen penetration depth in the absence of external diffusion limitation (cm) - Q volumetric oxygen uptake rate, (mmol O₂/l·h) - specific oxygen uptake rate (mmol O₂gm biomass (dry)·h) - r length coordinate (cm) - r_c oxygen penetration depth for sphere (cm) - r _c r_c in the absence of external diffusion limitation (cm) - r _c ^* oxygen penetration depth for cylinder (cm) - r _c ^* r _c ^* in the absence of external diffusion limitation (cm) - r_com combined mass transfer rate resistance (s) - r_d location where C_s becomes zero or C_cr (cm) - r_i radius of cylinder or sphere, half thickness of slab (cm) - U_sg superficial gas velocity (cm/s) - X cell concentration (g/l) Greek letters Thiele modulus, dimensionless - _L, _s liquid and solid phase volume fraction, respectively, dimensionless - effectiveness factor On sabbatical leave from KAIST, Seoul, Korea     

云南省丽蝇族二新种 (双翅目:丽蝇科)

本文报道的丽蝇族两新种,分别隶属于蜗蝇属(Melinda Robineau-Desvoidy,1830)和拟粉蝇属(Polleniopsis Townsend,1917),模式标本均保存在中国科学院上海昆虫研究所。 一、小黑蜗蝇Melinda nigrella 新种(图1—3)     

Dihydropyridine and phenylalkylamine receptors associated with cardiac and skeletal muscle calcium channels are structurally different

We have purified putative L-type Ca2+ channels from chick heart by virtue of their associated high affinity receptors for the Ca2+ channel effectors, dihydropyridines (DHPs), and phenylalkylamines (PAAs). A peptide of 185,000-190,000 daltons was found to comigrate with the peak of DHP binding activity during purification through two successive cycles of lectin affinity chromatography and sucrose density gradient centrifugation. A previously described peptide of 140,000 daltons, whose Mr was increased to approximately 180,000 under nonreducing conditions, also copurified with the 185-kDa peptide and dihydropyridine binding activity. When cardiac membranes were photolabeled with either the dihydropyridine [3H]azidopine or the PAA [3H]azidopamil prior to purification, a single, specifically labeled component of 185,000-190,000 daltons was present in the purified fractions. The properties of this 185-kDa cardiac DHP/PAA receptor were compared to the smaller 165-kDa DHP/PAA receptor previously purified from skeletal muscle. Antibodies raised against the 165-kDa skeletal muscle DHP/PAA receptor reacted with both rabbit and chick skeletal muscle receptors, but only poorly recognized, if at all, the cardiac 185-190 kDa component. The 185-kDa peptide present in the purified fractions obtained from cardiac muscle did not undergo substantial phosphorylation by cAMP-dependent protein kinase, while the purified 165-kDa peptide from rabbit and chick skeletal muscle was a good substrate for this kinase. The results show that the DHP and PAA receptors in cardiac muscle are contained in a 185-190-kDa peptide that is significantly larger than, and structurally and immunologically different from, it skeletal muscle counterpart.     

cDNA and deduced primary structure of rat protein B23, a nucleolar protein containing highly conserved sequences

Protein B23 (Mr/pI = 38,000/5.1) is a major RNA-associated nucleolar phosphoprotein which contains highly acidic segments and has a high affinity for silver ions. Using synthetic oligonucleotides as probes cloned cDNAs encoding protein B23 were isolated and characterized. One of the cDNAs, obtained from a rat brain library, contained an insert of 1232 base pairs of DNA encoding a polypeptide of 292 amino acid residues. Segments of the protein sequence were confirmed by partial sequencing of CNBr fragments from rat hepatoma protein B23. The protein contains a methionine-rich amino-terminal sequence and two highly acidic segments in the center of the sequence. The first acidic segment, in which 11 of the 13 residues are acidic, begins at residue 120 and contains a major phosphorylation site. In the second segment (residues 159-187) there are four copies of the sequence Asp-Asp-Glu, and all but two of the 29 residues have acidic side chains. When the sequence of the rat protein was compared with available sequences from other species a high degree of conservation was found; the 77-residue carboxyl-terminal sequence is identical with that of human protein B23 (Chan, P. K., Chan, W.-Y., Yung, B. Y. M., Cook, R. G., Aldrich, M. B., Ku, D., Goldknopf, I. L., and Busch, H. (1986) J. Biol. Chem. 261, 14335-24341), and about 63% of the residues are identical when the rat B23 sequence is compared with protein N038 from Xenopus laevis (Schmidt-Zachmann, M. S., Hügle-D?rr, B., and Franke, W. (1987) EMBO J. 6, 1881-1890). Except for the presence of highly acidic regions no significant similarities were found with protein C23 (nucleolin), the other major nucleolar protein.