Search PubMed⌕ Search

Biomedical subjects

D Lancet

Publications and source records attributed to D Lancet.

At least 91 records · Page 5Linked to original sources
PubMed1986

Changes in olfactory acuity induced by total inferior turbinectomy.

The short-term and long-term effects of total inferior turbinectomy on smell acuity was assessed in two groups of patients. Olfactory thresholds were determined by a three-way forced-choice method, using four odorants. Resection of obstructive inferior turbinates resulted in a decrease in olfactory thresholds in 22 of 24 tested patients. No deleterious effect on smell acuity was observed in 16 patients tested 2 1/2 years or more after surgery. Subjective assessment of olfactory acuity is unreliable. It is our intention to focus attention on an aspect of intranasal surgery not frequently reported.

Adolescent↗
PubMed1986

Olfactory GTP-binding protein: signal-transducing polypeptide of vertebrate chemosensory neurons.

The sense of smell involves the stimulation of sensory neurons by odorants to produce depolarization and action potentials. We show that olfactory responses may be mediated by a GTP-binding protein (G protein), a homolog of the visual, hormonal, and brain signal transducing polypeptides. The olfactory G protein is identified in isolated dendritic membranes (olfactory cilia preparations) of chemosensory neurons from three vertebrate species and is shown to mediate the stimulation by odorants of the highly active adenylate cyclase in these membranes. The G protein of olfactory neurons is most similar to Gs, the hormonal stimulatory GTP-binding protein. Its alpha subunit has a molecular weight of about 42,000, and it undergoes ADP-ribosylation catalyzed by cholera toxin that leads to adenylate cyclase activation. The slight difference in molecular weights of the frog olfactory and the liver Gs alpha subunits and the higher sensitivity of olfactory adenylate cyclase to nonhydrolyzable GTP analogs are consistent with the possible existence of different Gs variants. Signal amplification due to the olfactory G protein may be responsible for the unusual acuity of the sense of smell.

Adenosine Diphosphate Ribose↗
PubMed1986

Cyclic AMP-dependent protein phosphorylation in chemosensory neurons: identification of cyclic nucleotide-regulated phosphoproteins in olfactory cilia.

Chemosensory dendritic membranes (olfactory cilia) contain protein kinase activity that is stimulated by cyclic AMP and more efficiently by the nonhydrolyzable GTP analog guanosine-5'-O-(3-thio)triphosphate (GTP gamma S). In control nonsensory (respiratory) cilia, the cyclic AMP-dependent protein kinase is practically GTP gamma S-insensitive. GTP gamma S activation of the olfactory enzyme appears to be mediated by a stimulatory GTP-binding protein (G-protein) and adenylate cyclase previously shown to be enriched in the sensory membranes. Protein kinase C activity cannot be detected in the chemosensory cilia preparation under the conditions tested. Incubation of olfactory cilia with [gamma-32P]ATP leads to the incorporation of [32P]phosphate into many polypeptides, four of which undergo covalent modification in a cyclic nucleotide-dependent manner. The phosphorylation of one polypeptide, pp24, is strongly and specifically enhanced by cyclic AMP at concentrations lower than 1 microM. This phosphoprotein is not present in respiratory cilia, but is seen also in membranes prepared from olfactory neuroepithelium after cilia removal. Cyclic AMP-dependent protein kinase and phosphoprotein pp24 may be candidate components of the molecular machinery that transduces odor signals.

Animals↗
PubMed1986

Isolated frog olfactory cilia: a preparation of dendritic membranes from chemosensory neurons.

The recently introduced frog olfactory cilia preparation (Chen and Lancet, 1984; Pace et al., 1985) has been useful for studies of molecular chemosensory mechanisms. Here we describe in detail the properties of this cilia preparation. The "calcium shock" procedure leads to a complete removal of the cilia from the olfactory epithelial surface. Isolated cilia constitute segments of proximal regions with 9 X 2 + 2 microtubular arrangement and a large proportion of membrane vesicles, probably derived from the ciliary distal segments. Polypeptides unique to the olfactory cilia preparation, compared to a control preparation of palate respiratory cilia, are identified by Coomassie brilliant blue staining, silver staining, and radiolabeled lectin overlays, as well as by biosynthetic labeling with 35S-methionine in epithelial explants and protein phosphorylation in isolated cilia. The olfactory cilia preparation contains odorant-sensitive adenylate cyclase, which is absent in control membranes from deciliated epithelium. High activities of tyrosine and serine/threonine protein kinases are also present. The olfactory cilia preparation described should be instrumental in the further elucidation of the biochemistry and molecular biology of vertebrate olfaction.

Adenylyl Cyclases↗
PubMed1985

An inexpensive microcomputer-based image-analysis system: novel applications to quantitative autoradiography.

We describe a relatively inexpensive, yet versatile and powerful microcomputer-based image-analysis system, and its applications to processing of deoxyglucose autoradiographic data. Images are acquired via a video camera mounted on a light microscope or a light box, and digitized in 40 ms to 512 X 512 picture elements with 8-bit resolution (256 gray levels). The bit-mapped image analysis hardware can provide up to 256 colors for pseudo-color coding, and virtually instantaneous readout of brightness values for densitometry. The system is controlled by an 8-bit S-100 bus microcomputer, providing flexibility and ease of expansion. In addition to pseudo-color coding and densitometry, we have developed programs for averaging of successive sections, image subtraction and quantitative reconstruction of different planes of section from serial autoradiograms.

Animals↗
PubMed1984

Membrane proteins unique to vertebrate olfactory cilia: candidates for sensory receptor molecules.

In search for olfactory receptor molecules, we carried out comprehensive electrophoretic mapping of membrane proteins in the cilia of frog olfactory epithelium. Seven polypeptides, extracted from isolated cilia by nonionic detergent, were unique to the sensory organelles, compared to nonsensory (respiratory) counterparts. Olfactory cilia contained 3-10 times more membrane-associated protein as compared to respiratory cilia, in agreement with reported densities of freeze-fracture intramembranous particles. Four of the olfactory polypeptides were major constituents of the ciliary membrane, each amounting to greater than 10% of its total protein. Three major and one minor specific polypeptide were glycosylated, whereas membranes of nonsensory cilia were practically devoid of glycoproteins. A clear difference in surface composition was also shown by microscopic visualization of fluoresceinated lectin bound to intact isolated cilia. Two of the olfactory glycoproteins displayed pronounced heterogeneity of apparent molecular weight, which could partly be due to protein sequence diversity, as expected for odorant receptor molecules. The recently described inhibition of odorant-evoked sensory potentials by the lectin concanavalin A is consistent with the hypothesis that one or more of the specific glycoproteins described here plays a role in olfactory reception.

Animals↗
PubMed1982

Mapping of odor-related neuronal activity in the olfactory bulb by high-resolution 2-deoxyglucose autoradiography.

The spatial distribution of odor-induced neuronal activity in the olfactory bulb, the first relay station of the olfactory pathway, is believed to reflect important aspects of chemosensory coding. We report here the application of high-resolution 2-deoxyglucose autoradiography to the mapping of spatial patterns of metabolic activity at the level of single neurons in the olfactory bulb. It was found that glomeruli, which are synaptic complexes containing the first synaptic relay, tend to be uniformly active or inactive during odor exposure. Differential 2-deoxyglucose uptake was also observed in the somata of projection neurons (mitral cells) and interneurons (periglomerular and granule cells). This confirms and extends our previous studies in which odor-specific laminar and focal uptake patterns were revealed by the conventional x-ray film 2-deoxyglucose method due to Sokoloff and colleagues [Sokoloff, L., Reivich, M., Kennedy, C., DesRosiers, M. H., Patlak, C. S., Pettigrew, K. D., Sakurada, O. & Shinohara, M. (1977) J. Neurochem. 28, 897--916]. Based on results obtained by the two methods, it is suggested that the glomerulus as a whole serves as a functional unit of activity. The high-resolution results are interpreted in terms of the well-characterized synaptic organization of the olfactory bulb and also serve to illustrate the capability of the 2-deoxyglucose autoradiographic technique to map metabolic activity in single neurons of the vertebrate central nervous system.

Animals↗
PubMed1979

Complete amino acid sequence of a papain-solubilized human histocompatibility antigen, HLA-B7. 2. Sequence determination and search for homologies.

The complete amino acid sequence of the papain-solubilized heavy chain of a human histocompatibility antigen (HLA-B7) has been elucidated. It consists of a polypeptide of 271 residues (31 333 daltons). A single glycan moiety is attached to an asparagine residue at position 86 by an N-glycosidic bond. Two intrachain disulfide bonds, arranged linearly, involve half-cystine residues at positions 101 and 164 and at positions 203 and 259. They form two loops of 62 and 55 residues, respectively, separated by 38 residues. Computer analysis of the sequence suggests the existence of internal homology between the amino-terminal portion (residues 1--90) and the region of the first disulfide loop (residues 91--180). There is a significant homology between the second disulfide loop region of the chain (residues 182-271) and immunoglobulin (Ig) constant domains and beta 2-microglobulin [Orr, H. T., Lancet, D., Robb, R. J., López de Castro, J. A., & Strominger, J. L. (1979A) Nature (London) (in press)]. However, no such homology to Ig is apparent in the amino-terminal or in the first disulfide loop regions.

Amino Acid Sequence↗
PubMed1979

The heavy chain of human histocompatibility antigen HLA-B7 contains an immunoglobulin-like region.

The 88-residue fragment (ac-2) containing the second disulphide loop from HLA-B7 heavy chain is shown to have statistically significant homology with Ig constant domains, including both matches at invariant positions and conservative substitutions of structurally important residues. Thus, both the light chain (beta 2m) and a segment of the heavy chain of HLA antigens may be structurally and evolutionarily related to immunoglobulins.

Amino Acid Sequence↗
PubMed1979

Folding pathways of immunoglobulin domains. The folding kinetics of the Cgamma3 domain of human IgG1.

The in vitro folding kinetics of a fragment corresponding to an intact dimer of the Cgamma3 domain of human IgG1 (pFc') were monitored via the large changes in tryptophan fluorescence which accompany these processes. In going from the guanidine hydrochloride (Gdn.HCl) induced unfolded state (4.0 M Gdn.HCl) to the native state (0.5 M Gdn.HCl), three well-separated first-order processes were observed having time constants of 5, 50, and 350 s and roughly equal amplitudes. These values were concentration independent, a fact consistent with there being no fluorescence change accompanying dimerization. These time constants are one to two orders of magnitude slower than those observed for proteins of similar size such as ribonuclease or cytochrome c, most probably reflecting the complex processes involved in forming the correct beta-sheet arrangement of immunoglobulin domains. The corresponding unfolding transition is biphasic having time constant values of 50 and 500 s, the latter comprising 80% of the fluorescence change. These data indicate the presence of at least one species with intermediate fluorescence along the unfolding pathway. Gdn.HCl concentration jumps were also performed over various intervals within the transition zone. The results are not consistent with a fully reversible mechanism. In the absence of the intrachain disulfide bond, pFc' exists in an unfolded state even at 0.5 M Gdn.HCl. In a concomitant refolding and reoxidation experiment (at 0.5 M Gdn.HCl and using an optimal disulfide interchange catalytic system), the time constant for disulfide formation was in the range of 80--200 s and the fluorescence change revealed a lag phase analyzable in terms of rate-limiting reoxidation and refolding times consistent with those observed for the initially disulfide bonded species. Under similar conditions but a 4 M Gdn.HCl, reoxidation was more than two orders of magnitude slower, suggesting that reoxidation is directed by a refolding nucleation event.

Disulfides↗
PubMed1979

Heavy chain of HLA-A and HLA-B antigens is conformationally labile: a possible role for beta 2-microglobulin.

The three-dimensional organization of HLA antigens has been investigated by spectroscopic and immunochemical techniques. Measurement of the circular dichroism shows that in papain-solubilized HLA the heavy chain as well as the previously studied light chain (beta 2-microglobulin) consists predominantly of beta-pleated sheet structures. When heavy chain is separated from the light chain under denaturing conditions and is allowed to renature, about 50% of the beta structure is lost, concomitantly with most of the alloantigenic activity. Analysis of the two acid-cleaved fragments of HLA-B7 heavy chain shows that beta structure is preferentially lost from the COOH-terminal region of the heavy chain. Exposure to denaturants per se does not inevitably result in irreversible loss of antigenic activity. However, recovery of antigenic properties does seem to depend on reassociation of the two chains. The results reported here provide further evidence for (i) the similarity of HLA antigens and immunoglobulins at the three-dimensional level and (ii) two distinct and physiologically important conformations of the HLA heavy chain, depending upon whether it is associated with the light chain.

Beta-Globulins↗
PubMed1978

Hapten-linked conformational equilibria in immunolglobulins XRPC-24 and J-539 observed by chemical relaxation.

The interaction of oligogalactan haptens with the murine myeloma proteins XRPC-24 and J-539 has been investigated by the fluorescence temperature-jump method. The relaxation spectrum is composed of two processes, the faster representing hapten assocaition and the slower a protein isomerization. In both cases the concentration dependence of relaxation times and amplitudes was consistent with the general mechanism formulated by Lancet and Pecht (1976, Proc. Natl. Acad. Sci. U.S.A. 73:3549), in which the equilibrium between two conformations of the protein is shifted by hapten binding. The intact proteins and their Fab fragment had identical kinetic behavior, indicating that the conformational changes are located in the Fab region. Temperature dependence analysis for protein J-539 permitted the calculation of activation parameters and led to a consistent energy profile for all the elementary steps. The conformational states are separated by large activation barriers, but have similar free energies. The results suggest that hapten-induced conformational changes in immunoglobulins are more general phenomena than was previously thought.

Animals↗