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Biomedical subjects

B A Lewis

Publications and source records attributed to B A Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1985

Magnetic birefringence studies of dilute purple membrane suspensions.

We have observed the magnetically induced orientation of purple membrane suspensions by measuring the birefringence as a function of concentration and temperature at fields up to 10.5 Tesla (T). At these fields, the orientation approaches saturation even in dilute solutions; therefore, the birefringence data, together with an estimate of the membrane size distribution obtained from electron microscopy, permits one to determine the diamagnetic susceptibility anisotropy. We find delta chi mole = 1.2 +/- 0.3 X 10(-3) erg G-2mol-1 of bacteriorhodopsin. If delta chi were due only to the oriented peptide bonds of the transmembrane alpha helices, this experimental value would indicate that delta K, the anisotropy per mole of peptide bonds, is considerably larger than previously suggested. On the other hand, the large value for delta chi mole of bacteriorhodopsin can also be explained by a net orientation of the aromatic amino acid side chains of bacteriorhodopsin with their planes perpendicular to the membrane surface. In addition, the present data analysis demonstrates the critical dependence of the calculated delta chi value on the values for the membrane size distribution.

Bacteriorhodopsins↗
PubMed1985

Inhibition of Candida albicans by methanethiol produced by Brevibacterium linens.

Brevibacterium linens was screened for antifungal activity against Candida albicans using several antibiotic assay methods. The growth of C. albicans was inhibited only when the dual culture assay method was employed and using methionine-supplemented media. Results suggest that methanethiol which is produced by B. linens' utilization of methionine is the agent inhibitory to C. albicans' growth.

Brevibacterium↗
PubMed1985

Infectious drug resistance.

The emergence of antibiotic-resistant bacteria is a serious threat to public health. Infectious drug resistance, the transmission of resistant determinants from antibiotic-resistant bacteria to antibiotic-sensitive bacterial populations, creates clinical problems that must be addressed. Adequate knowledge of the mechanisms responsible for bacteria resistance is important for ensuring the benefits of antimicrobial therapy.

Anti-Bacterial Agents↗
PubMed1984

Hypothesis-testing and nonlinguistic symbolic abilities in language-impaired children.

This study sought to clarify further the cognitive abilities of language-impaired children by examining their hypothesis-testing and nonlinguistic symbolic abilities. A discrimination learning task and a concept formation task were used to measure hypothesis-testing abilities, and a haptic (touch) recognition task was used to assess nonlinguistic symbolic abilities. Subjects were 10 language-impaired and 10 language-normal children matched for performance Mental Age. Measures of expressive and receptive language were also obtained from each child. The language-impaired children were found to perform significantly poorer than their MA controls on the haptic recognition task and on a portion of the discrimination learning task. No differences were found between the two groups' concept formation abilities. Correlational analyses revealed a particularly strong positive relationship between performance on the Peabody Picture Vocabulary Test and the haptic recognition tasks. It was speculated that this relationship was motivated by the symbolic demands of these tasks. One implication of this speculation is that a symbolic representational deficit might better explain the receptive language deficit than the expressive one.

Age Factors↗
PubMed1983

Bacteriorhodopsin remains dispersed in fluid phospholipid bilayers over a wide range of bilayer thicknesses.

We have used vesicles made from delipidated bacteriorhodopsin and synthetic lecithins to address the following questions. If the transmembrane dimension of a protein hydrophobic surface differs from the equilibrium thickness of its lipid bilayer environment, will protein monomers aggregate to decrease the protein-lipid contact surface area? If so, how large must the difference be to induce aggregation? Using lecithins with acyl chains from di-10:0 to di-24:1, the thickness of the bilayer hydrocarbon region above the lipid phase transition temperature (tm) was varied from 14.5 A less than to 7.5 A more than the transmembrane dimension of the bacteriorhodopsin hydrophobic region. Bacteriorhodopsin remains dispersed when the surrounding bilayer hydrophobic region is 4 A thicker or 10 A thinner than the bacteriorhodopsin hydrophobic surface. Only the thin- (10:0) and thick- (24:1) bilayer samples showed any bacteriorhodopsin aggregation above tm. Thus a surprisingly large difference between protein and lipid hydrophobic thicknesses can be accommodated without protein aggregation. The lipid bilayer can evidently sustain large local distortions with a small change in free energy.

Bacteriorhodopsins↗
PubMed1983

Lipid bilayer thickness varies linearly with acyl chain length in fluid phosphatidylcholine vesicles.

The thickness of the lipid bilayer in vesicles made of pure phosphatidylcholines, with acyl chain lengths ranging from 10 to 24 carbons, has been determined by analysis of continuous X-ray scattering data from vesicle pellets at temperatures above the lipid phase transition temperature. Bilayer thickness was found to vary linearly with the number of carbons per acyl chain. The lines for saturated and monounsaturated acyl chains were slightly displaced but had similar slopes. For the saturated species di-12:0, di-14:0, di-16:0, and di-18:0 phosphatidylcholine the surface areas per molecule were all 65.7 to 66.5 A2, while the monounsaturated species and di-10:0 phosphatidylcholine all occupied 67.7 to 70.1 A2 per molecule.

Lipid Bilayers↗
PubMed1983

Structural studies of cytochrome P-450 using small angle x-ray scattering.

We have employed small angle x-ray scattering to examine the solution conformation of cytochrome P-450cam in the presence and absence of its substrate, camphor. The radius of gyration (Rg) of the protein is found to be 23.9 +/- 0.2 A in both states. Comparison of the radius of gyration with that expected for a spherical protein of the same molecular weight indicates that P-450 is an elongated molecule and that its shape may best be approximated by a cylinder about 30 A in diameter and 80 A in length.

Cytochrome P-450 Enzyme System↗
PubMed1983

Pair distribution functions of bacteriorhodopsin and rhodopsin in model bilayers.

The pair distribution functions have been measured from freeze-fracture pictures of bacteriorhodopsin and rhodopsin recombinants with diacyl phosphatidylcholines (PC) of various hydrocarbon chain lengths. Pictures were used of samples that had been frozen from above the phase transition temperature of the lipid. Measured functions were compared with those calculated from two model interparticle potential energy functions, (a) a hard-disk repulsion only, and (b) a hard-disk repulsion plus electrostatic repulsion for a point charge buried in the membrane. The measured functions for bacteriorhodopsin di 12:0 PC, di 14:0 PC, and di 16:0 PC recombinants can be simulated using an interparticle hard-disk repulsion only. Bleached rhodopsin di 12:0 PC and di 18:1 trans-PC recombinants, and dark-adapted rhodopsin di 10:0 PC recombinants yield functions that are better simulated by assuming an additional repulsive interaction. The measured functions resemble those calculated using the hard-disk plus electrostatic repulsion model. The picture of dark-adapted rhodopsin in di 18:1 trans-PC frozen from 20 degrees C shows partial aggregation that is apparent in the measured pair distribution function. This attractive interaction persists even at 37 degrees C, where the measured function shows deviations from the hard-disk repulsive model, indicative of an attractive interparticle interaction. Implications of these results are discussed in terms of protein-lipid interactions.

Bacteriorhodopsins↗
PubMed1983

The influence of dietary fiber source on human intestinal transit and stool output.

Wheat bran ground to a coarse and fine particle size, purified cellulose and ethanol-extracted cabbage fiber, fed to 24 adult males during an 80-day metabolic trial, were examined for effects on intestinal transit time, laxation and stool composition. Brilliant blue, plastic pellets, polyethylene glycol (PEG)-4000 and Cr(III) mordanted onto isolated bran fiber were simultaneously administered for transit measurements. Intersubject variability in response to fiber source was highly significant for all transit and stool measurements. Only coarse bran or cellulose addition increased transit speed (decreased transit time) over basal rates. Grinding of bran significantly reduced fecal output because of reduced fecal water. Only subjects consuming cellulose or fine bran reported difficult or uncomfortable defecations. Though cabbage produced the smallest fecal output, stools had a high moisture content comparable to those obtained from coarse bran, which suggests a large microbial output in response to a fermentable substrate. Significant negative correlations were produced when changes in dry matter or cell wall intakes were regressed with Cr (III) transit. These findings suggest that the level of either food or fiber in the diet are variables that influence intestinal transit time and should be controlled in studies measuring it. Increases in fiber intake linearly increased fecal output of water and dry matter. Regression slopes were characteristic of each fiber source.

Adult↗
PubMed1981

The radius of gyration of L-arabinose-binding protein decreases upon binding of ligand.

The technique of small angle x-ray scattering has been employed to study the effect of sugars on the radius of gyration of the L-arabinose-binding protein, a component of the high affinity L-arabinose transport system in Escherichia coli. We find that the binding of L-arabinose to the "sugar-free" protein in solution causes a 0.94 +/- 0.33 A decrease in the radius of gyration while D-glucose, a nonbinder, produces no such effect. The radius of gyration calculated from the complete atomic co-ordinates of the crystal structure of L-arabinose-binding protein (solved with bound L-arabinose) corresponds to the experimentally determined value for the radius of gyration in the presence of L-arabinose. This reduction in radius of gyration can be best accounted for in terms of a substrate-induced cleft closure in which one lobe rotates relative to the other lobe. A compute modeling study indicates that a rotation of 18 degrees about a hinge deep in the base of the sugar-binding cleft between the two domains would produce the observed decrease in the radius of gyration. The findings (Newcomer, M. E., Gilliland, G. L., and Quiocho, F. A. (1981) J. Biol. Chem. 256, 13213-13222) that the L-arabinose molecule embedded in the cleft between two domains is completely inaccessible to the solvent is consistent with a closing of the cleft between the two lobes.

Arabinose↗
PubMed1981

Urinary levels of blood group A trisaccharide: observations in two siblings with neuronal ceroid lipofuscinosis.

A readily detectable carbohydrate in the urine of two siblings with neuronal ceroid lipofuscinosis was found to be the blood group A trisaccharide. One child expired before blood typing was done while the other sibling was AB. This latter child excreted greater amounts of the trisaccharide than a group of blood type A subjects with different diagnoses when all the subjects were receiving whole or skim milk by nasogastric feedings. While the relevance of this observation to neuronal ceroid lipofuscinosis is unknown, it has been shown that the trisaccharide may be a major urinary carbohydrate depending on diet and blood type.

ABO Blood-Group System↗
PubMed1978

An equilibrium study of metal ion binding to human plasma coagulation factor XIII.

1. The binding of Ca2+ to plasma coagulation Factor XIII from man and from cow caused a small decrease in the intrinsic fluorescence of the protein with a dissociation constant of 0.1 mM. A similar decrease was observed with the thrombin-activated Factors (Factors XIIa). The decrease in protein fluorescence was also caused by both Ni2+ and Mn2+ but not by Mg2+. 2. 45Ca2+ binding was directly demonstrated by equilibrium dialysis. Ca2+ at 0.2 mM bound to Factor XIII (a2b2) and Factor XIIIa (a'2b2) but not to isolated b2-protein. A tight-binding site for Ca2+ is associated with the a-subunits. 3. The Ca2+ essential for the enzyme activity of Factor XIII from man, pig and cow can be replaced by Ni2+, Cu2+, La3+, Mn2+, Fe3+, Y3+, Co2+, Sr2+ or Tb3+, but not by Mg2+.

Animals↗
PubMed1978

Protein-protein interactions in blood clotting. The use of polarization of fluorescence to measure the dissociation of plasma factor XIIIa.

1. Human plasma Factor XIII (the precursor of fibrin-glutamine-fibrin-lysine endo-gamma-glutamyltransferase) was randomly labelled by incubation with fluorescein isothiocyanate. The biochemical properties of the system were unaltered by the label. The polarization of the fluorescein fluorescence attached to the plasma protein was measured and the following conclusions were reached. 2. Factor XIII (a'2b2) does not dissociate in the protein-concentration range 10-500 microgram/ml either with or without added Ca2+. 3. Factor XIIIa (a'2b2) does not dissociate in the absence of Ca2+ in the protein-concentration range 10-500 microgram/ml. 4. Additions of Ca2+ to Factor XIIIa result in a decreased polarization of fluorescence as the tetramer dissociates. The decrease in polarization was the same amplitude at protein concentrations 10-500 microgram/ml and Ca2+ concentrations 2-66 mM and indicates that the overall process is essentially irreversible. The decrease in polarization consisted of fast and slow exponential phases. Both the rate of the fast phase and the proportion of the reaction it represented increased with Ca2+ concentration. 5. A comparison of the rate of dissociation measured by fluorescence polarization and the rate of appearance of enzyme activity in the presence of a protein substrate suggests that the Factor XIII is autoactivated by a soluble a-subunit-containing molecular forming a tight complex with the substrate.

Blood Proteins↗
PubMed1978

Physical and biological properties of structural and other nondigestible carbohydrates.

Selected characteristics of dietary fiber and associated nondigestible polysaccharides are discussed. These properties, which could alter gastrointestinal function, include particle size, solubility and viscosity, and interactions with small organic compounds, cations, salts, and proteins. The relationship between structure and the physiochemical properties is indicated.

Cellulose↗