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Biomedical subjects

I C Smith

Publications and source records attributed to I C Smith.

At least 181 records · Page 10Linked to original sources
PubMed1980

Molecular dynamics of sugars bound to wheat germ agglutinin, as studied by deuterium nuclear magnetic resonance.

Deuterium nuclear magnetic resonance is used to delineate the molecular dynamics of sugars bound to a lectin. 2H spin-spin relaxation times (from linewidth measurements) and reorientational correlation times are determined for N-acetylglucosamine specifically-labeled with 2H in the N-acetyl group and at carbon-3 of the pyranoside ring, in the presence and absence of wheat germ agglutinin. The correlation time for the 2H-label of N-acetylglucosamine-3-2H in the bound state is the same as that of the protein (3 X 10(-8)S), indicating that the six-membered ring has negligible motional freedom relative to the protein. The correlation time for the C2H3 group of N-acetyl-2H3-glucosamine (1.7 X 10(-9)S) shows that the N-acetyl side chain is also immobilized in the binding site, the only motion available being rotation of the C2H3 group about its threefold axis.

Acetylglucosamine↗
PubMed1980

Degradation of enkephalin and enkephalinamide by neuroblastoma x glioma hybrid cells as studied by 13C n.m.r.

13C n.m.r. and thin-layer chromatography were used to monitor the degradation of methionine-enkephalinamide in the presence of neuroblastoma x glioma hybrid cells (NG 108-15) and membranes. Puromycin and trypsin treatment failed to protect enkephalinamide from degradation over long periods of time (up to 24 hours). The major degradation products of [3[2-13C]glycine] methionine-enkephalinamide observed by 13 C n.m.r. showed glycine-3 in a non-terminal position, an N-terminal position and free glycine. A minor component showed glycine-3 in a C-terminal position.

Cell Membrane↗
PubMed1980

31P NMR studies of vegetative and encysted cells of Acanthamoeba castellanii. Observation of phosphonic acids in live cells.

31P NMR studies have been performed on vegetative and encysted Acanthamoeba castellanii. A prominent feature of the spectra is the presence of resonances characteristic of P-C linkages. Vegetative cells show sharp phosphonate resonances whereas encysted cells show broad phosphonate resonances and narrow phosphate resonances. Studies of model compounds using 31P NMR have shown the narrow resonances to arise from 2-aminoethylphosphonic acid; the broad components from encysted cells arise from molecules with long rotational correlation times such as aggregates of lipophosphonoglycan or phosphonoprotein. Vegetative cells also show the presence of an electronegatively beta-substituted phosphonic acid, possibly 1-hydroxy-2-aminoethylphosphonic acid, a component identified in the cell membrane lipophosphoglycan. pH titration studies of a number of phosphonic acid model compounds show a chemical shift behaviour quite distinct from that of biological phosphates. Upon acidification from pH 12, resonances shift to high field followed by return to lower field at pH 1.0. These resonances can be ambiguous as monitors of cellular pH. The pH of both vegetative and encysted cells is 6.0--6.5. Encysted cells under anaerobic conditions show no spectral changes over 24 h. Vegetative cells under similar conditions show time-dependent changes characteristic of variation in cellular pH. There appears to be little correlation between pH and the variously differentiated states (vegetative or encysted) in Acanthamoeba.

Amoeba↗
PubMed1980

Multiple binding sites for local anesthetics in membranes: characterization of the sites and their equilibria by deuterium NMR of specifically deuterated procaine and tetracaine.

Anesthetics bound to model membranes were observed directly by means of deuterium nuclear magnetic resonance (NMR). The specifically deuterated local anesthetics procaine and tetracaine were synthesized, and their partition coefficients (water:phosphatidylcholine) and pKa values determined. The interaction of these anesthetics with lamellar dispersions of egg phosphatidylcholine was studied by 2H nuclear magnetic resonance and by electron spin resonance (ESR) of a spin-labelled phospholipid at low (5.5) and high (9.5) pH. The ESR experiments suggest that tetracaine intercalates in the membrane and that it equilibrates between water and the phospholipid bilayers of the multilamellar system. The NMR results are consistent with a model where the anesthetic is (1) free in water, (2) weakly bound, and (3) strongly bound to the membrane. A fast exchange exists between the two first sites, but exchange is slow with the third site. Binding of type 3 is observed only at high pH for procaine, whereas it is found both at low and high pH for tetracaine. Calculations of the partition coefficients for the charged and uncharged forms of tetracaine indicate that both sites, 2 and 3, are occupied by the charged form at low pH and by the uncharged form at high pH. The partition coefficient for the weakly bound species was estimated from an analysis of the dependence of line width on the lipid to water ratio. The NMR data suggest that the binding sites for the strongly bound charged and uncharged species are different, the former probably being closer to the membrane-water interface. Estimates of molecular order parameters for the strongly bound species indicate that it is located with its long molecular axis approximately parallel to the director for ordering of the fatty acyl chains. A small increase in lipid ordering by tetracaine is observed at low pH, as evidenced by 2H NMR of the deuterated N-methyl groups of phosphatidylcholine; the reverse occurs at high pH.

Deuterium↗
PubMed1979

Lipid reorganization in biological membranes: a study by Fourier transform infrared difference spectroscopy.

The first application of infrared difference spectroscopy to the study of a natural biological membrane is described. Perdeuterated palmitic acid was incorporated biosynthetically into the lipids of the plasma membrane of Acholeplasma laidlawii and the temperature-induced structural rearrangement of the endogenous lipids monitored via their C--2H vibrational modes. Changes in infrared parameters were studied between 0 and 50 degrees C and contrasted with those occurring in the model membrane system of 1,2-diperdeuteropalmitoyl-sn-glycero-3-phosphocholine. The phase transition of the biomembrane occurs over a 20 degrees C range with the temperature of the maximum rate of change of absorbance coinciding with that of the sharp phase transition of the model membrane.

Acholeplasma laidlawii↗
PubMed1979

Determination, by carbon-13 nuclear magnetic resonance spectroscopy, of the composition of glucans synthesized by enzymes of the cariogenic organism Streptococcus mutans.

The 13C-n.m.r. spectra of water-soluble and -insoluble glucans synthesized by enzymes isolated from six strains of Streptococcus mutans are interpreted. The glucans are shown to be composed primarily of alpha-(1 linked to 3)- and alpha-(1 linked to 6)-linked glucosyl residues, and the relative abundance of each linkage is estimated from peak areas. Treatment of water-insoluble glucans with dextranase is found to result in water-soluble and -insoluble products, the former enriched in alpha-(1 linked to 6)-linkages and the latter in alpha-(1 linked to 3)-linkages. The structural conclusions arrived at by 13C-n.m.r. spectroscopy are consistent with data from methylation analysis and 1H-n.m.r. spectroscopy.

Chemical Phenomena↗
PubMed1979

Effects of D and L amino acid residues in linear peptides on carbon-13 nuclear magnetic resonance parameters.

The 13C spectra of the linear tripeptidyl diastereoisomers, Gly-Gly-Leu, Gly-Gly-D-Leu, Leu-Gly-Gly, D-Leu-Gly-Gly, Ala3, Ala-Ala-D-Ala, Ala-D-Ala-Ala, Val3, and Val-Val-D-Val are very similar or even identical at pH meter readings of 1.0, 7.0 and 12.0 in D2O. The spectra of Pro-Leu-Gly-NH2 and Pro-D-Leu-Gly-NH2 likewise show only minor differences in 13C chemical shifts (less than 0.4 p.p.m.) under similar conditions. This contrasts significantly with previous findings comparing 13C chemical shifts of cyclo(Pro-Leu) and cyclo(Pro-D-Leu) where major differences in chemical shifts were observed for both residues due to differences in conformational constraints present in these cyclic proline-containing peptides. The least-squares fit of spin-lattice relaxation times (T1) for Pro-Leu-Gly-NH2 and Pro-D-Leu-Gly-NH2 show that it is not possible to fit all the T1 values to a unique and rigid structure whether folded or extended. The glycyl residue undergoes enhanced motion when compared with the prolyl and leucyl residues. Internal motion must be postulated within the proline ring and for the CH3 groups of leucine.

Amino Acid Sequence↗
PubMed1979

The electrogenic potential in rat C nerve fibres: some effects of lithium and thallium.

1. Subsequent to bathing a desheathed vagus nerve in a K-free medium Li (5-50 mM) generates a hyperpolarizing response in the same manner as does K except that Li is 23 times less potent than K. Preincubation with small concentrations of either Li or K inhibits a subsequent K response.2. The Li response is less phasic than the K response. In the presence of a cardiac glycoside Li has no effect whereas K depolarizes the preparation. Thus Li is presumed to generate a relatively pure ouabain-sensitive electrogenic response.3. If a Li response is always terminated with 50 mM-Li, but various concentrations are used during the first half, the total response has a constant area despite the wide range of activation during the first half. This implies that the electrogenic pump ratio is constant over this range of activation.4. Thallium (1 mM) also generates a ouabain-sensitive response, but even short exposures (5 min) produces a strong and lasting inhibition of subsequent potassium responses. On a slower time scale Tl also inhibits the electrogenic post-tetanic hyperpolarization. After exposure to Tl a test action potential shows that the afterpotential is also decreased.5. If action potentials are produced during an electrogenic response the hyperpolarizing afterpotential reverses polarity. It is supposed that this is due to a short-circuiting of the electrogenic potential during this time.

Action Potentials↗