Monoclonal antibodies to the main immunogenic region of the nicotinic acetylcholine receptor bind to residues 61-76 of the alpha subunit

Monoclonal antibodies (mAbs) to the main immunogenic region (MIR) bind to fusion proteins containing region 37-200 of the alpha chain of Torpedo, mouse, and chicken nicotinic acetylcholine receptor. In the case of the mouse alpha chain, these mAbs react with sequence 61-216 but not with 74-216. A synthetic peptide M1, containing residues 61-76 of the mouse alpha chain, also binds these anti-MIR mAbs, showing that all or part of their binding site is included in this region. The conformational dependence and epitope specificity of the mAbs are discussed.     

Tritiated borohydride reduction of carbohydrates: reduction of individual monosaccharides, alone or in groups, results in highly divergent specific activities.

Reduction of carbohydrates by tritiated borohydride resulted in the production of alditols or glycosides with characteristically divergent specific radioactivities. Simultaneous reduction of individual sugars in the presence of a reference standard, talose, permitted the assignment of a unique specific radioactivity with respect to talitol as 100%. A variety of structures was examined, including neutral hexoses, free and acetylated aminosugars, ketohexoses and glycosides containing a fixed pyranose ring adjacent to a carbonyl group. In the latter case, the resulting steric hindrance severely restricted the incorporation of tritium. In both of the ketohexoses tested, the minor product of the two epimeric alditols exhibited the higher specific radioactivity. In all cases, reduction produced a characteristic and reproducible specific activity in which the values varied from 51 to 182% of that found for talose. These results are interpreted on the basis of generalizations concerning mechanism and predictive value.     

Host-Symbiont Specificity Expressed during Early Adsorption of Rhizobium meliloti to the Root Surface of Alfalfa

Early (4 h) adsorption of Rhizobium meliloti L5-30 in low numbers to alfalfa roots in mineral solution was examined for competition with other bacterial strains. All tested competitor strains decreased the adsorption of L5-30 by extents which depended on the strain and its concentration. The decrease of adsorption by R. meliloti competitors (all of them infective in alfalfa) was nearly complete at saturation (97 to 99% decrease). All other heterologous rhizobia and Agrobacterium tumefaciens at saturating concentrations (10⁶ to 10⁷ per ml) decreased adsorption of L5-30 only partially, less than 60%. The differential effects of homologous and heterologous competitors indicate that initial adsorption of R. meliloti to the root surface of its host occurs in symbiont-specific as well as nonspecific modes and suggest the existence of binding sites on roots which are highly selective for the specific microsymbiont in the presence of other heterologous bacteria even in very unfavorable (less than 10⁻⁴) symbiont-competitor concentration ratios.     

The nifHDK genes are contiguous with a nifA-like regulatory gene in Rhodobacter capsulatus

Summary A 15.2 kb DNA fragment was isolated from Rhodobacter capsulatus (ex. Rhodopseudomonas capsulata), which was able to complement mutations both in a nifA-like regulatory gene and in the nifH gene. Physical mapping of this fragment revealed that the nifA-like gene was adjacent to, and downstream from, the nifHDK operon. Hybridization experiments were carried out using a cloned Klebsiella pneumoniae DNA fragment containing nifA and the flanking portions of nifB and nifL. This fragment failed to hybridize with a 2.15 kb HindIII fragment of R. capsulatus DNA containing the nifA-like gene, but hybridized instead with a 2.6 kb EcoRI fragment adjacent to the nifA-like gene. The homologous region was found to be located within the K. pneumoniae nifB gene. The adjacent 2.6 kb and 2.15 kb fragments also hybridized with each other, indicating the presence of repeated sequences in this region.     

Gastric mucosal binding studies with enprostil: A potent anti-ulcer prostaglandin

The potent antiulcer prostaglandin enprostil binds with high affinity to porcine gastic mucosal tissues. This binding is saturable, dissociable and displaceable by compounds with similar structures. Various characteristics of binding such as pH optimum and displacement potencies suggest that enprostil binds to mucosal PGE₂ sites. Structure-activity and gastric mucosal binding relationships were also examined.     

Tracer diffusion coefficients of proteins by means of holographic relaxation spectroscopy: application to bovine serum albumin

Holographic relaxation spectroscopy has been used to measure tracer diffusion coefficients for photochromically labeled bovine serum albumin in solutions having total bovine serum albumin concentrations in the range 3.25 to 257 g/liter. In the limit of zero concentration, the diffusion coefficient (20 degrees C, 0.1 M NaCl, 0.05 M Tris, pH 8.0) was found to be (5.9 +/- 0.1) X 10(-7) cm2/s and the initial slope was zero. The concentration dependence of the diffusion coefficient was not significantly affected by the fraction of protein molecules which were labeled. Holographic relaxation spectroscopy permits rapid, accurate determination of tracer diffusion coefficients for proteins in mixtures.     

Ion-pair reverse-phase high-performance liquid chromatography. Application to the study of chicken liver NAD+ kinase

An ion-pair, reverse-phase, high-performance liquid chromatography method of assay was developed and used in a series of rate studies carried out with the enzyme chicken liver NAD+ kinase (ATP:NAD+ 2'-phosphotransferase, EC 2.7.1.23). Complete separation of all products and reactants was achieved within 15 min. ATP, NAD+, ADP, and NADP+ were monitored at 260 nm as they eluted from a Zorbax (Dupont) ODS (4.6 X 250-mm) column using an acetonitrile and 0.01 mM NH4(H2PO4)/0.005 M tetrabutylammonium phosphate (pH 7.0) gradient. The enzyme shows a marked preference for ATP (and dATP) and Mg2+ (or Mn2+) relative to other trinucleotides and divalent metal ions. It exhibits residual adenylate kinase and ATPase activity, but no NADH kinase activity. When polyphosphate replaced ATP, NADP+ production dropped to 2.5%. The addition of Ca2+ and/or bovine brain calmodulin did not significantly enhance the rate of NADP+ production.     

Uptake of glycine by excised pulvini of Mimosa pudica in relation to proton pump activity

Uptake of [³H]-glycine by sections of Mimosa pudica L. pulvini is pH dependent (maximum at pH 5.5) and exhibits biphasic saturation kinetics in the range of concentrations tested (1–75 m M ). Effects of compounds which increase [fusicoccin (FC)] or decrease (uncouplers, ATPase inhibitors) the proton-motive force were tested both on the pH variations induced in the incubation medium and on glycine uptake by the pulvinar tissues: there is a close relationship between the time required for the effect of these compounds on the acidification (for FC) and the pH rise (for the inhibitors) of the medium and that needed respectively for promotion and inhibition of glycine uptake. Experiments with sulfhydryl-reacting compounds show that N-ethylmaleimide induces a large rise in pH in the incubation medium and strongly inhibits glycine uptake, whereas p -chloromercuribenzenesulfonic acid has less effect on these processes. These results argue for a proton-glycine symport mechanism in the pulvinar tissue and thus support the previously postulated involvement of a proton pump in the regulation of pulvinar movement.     

Dielectric behavior of DNA solution at radio and microwave frequencies (at 20 degrees C).

The dielectric constant and conductivity of calf thymus DNA were investigated at frequencies between 0.1 MHz and 70 GHz. This work is to investigate the dielectric properties of DNA in low gigahertz region and also to study whether the dielectric behavior of the water is affected by the presence of highly charged DNA. The results of these measurements indicate the presence of two anomalous dispersions, the one between 1 MHz and 1 GHz and the second one above 1 GHZ. The dispersion at low frequencies is likely to arise from polar groups in the DNA molecule. The relaxation behavior of unbound water in DNA solution is only slightly affected by the presence of DNA at concentrations below 1%.     

Lectin binding sites in the vitelline envelope of Bufo arenarum oocytes: Role in fertilization

Incubation of dejellied spawned oocytes from Bufo arenarum with different lectins results in a decrease of oocyte fertility. Concanavalin A was the most effective lectin; phytohem-agglutinin P and wheat germ lectin were less effective. Agglutinin from soybean was scarcely active. These lectin effects could be ascribed to a hindering of specific sites for some proteases, since the same treatment renders the oocyte vitelline envelope insensitive to spermatolysin (an essential requisite for fertilization) and to trypsin. Also in this case concanavalin A was the most effective lectin. Univalent concanavalin A was also effective in blocking the fertility of dejellied oocytes. These results indicate that the residues of α-D-glucose and α-D-mannose present in the vitelline envelope are involved in gamete interactions in Bufo arenarum. This idea is also supported by the finding that dejellied oocytes (fertilizables) have a number of binding sites for concanavalin A that is three or four orders of magnitude higher than coelomic or fertilized oocytes (both not penetrable by spermatozoa).