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Biomedical subjects

L J Bishop

Publications and source records attributed to L J Bishop.

12 recordsLinked to original sources
PubMed1997

Randomized, double-blind, placebo-controlled, consumer rechallenge test of Olean salted snacks.

Olestra is a zero-calorie fat substitute that is neither digested nor absorbed. A randomized, double-blind, placebo-controlled, within-subject, crossover rechallenge study was conducted to compare the occurrence of gastrointestinal symptoms after ingestion of chips made with Olean brand of olestra or conventional triglycerides in subjects who had previously experienced gastrointestinal symptoms they attributed to consuming Olean. A total of 57 male or female subjects received 2 oz of Olean potato chips or triglyceride potato chips at each of four weekly site visits. The occurrence of gastrointestinal effects after product consumption was noted in follow-up telephone interviews 3 to 5 days after each visit. There was no significant difference in the frequency of any gastrointestinal symptoms (abdominal cramping, diarrhea, loose stools) following consumption of Olean chips or triglyceride chips, and the severity of diarrhea, loose stools, and abdominal cramping was similar. We conclude that consumption of a 2-oz serving of Olean chips is no more likely to result in reports of gastrointestinal symptoms than consumption of triglyceride snacks as a part of the usual diet, even in individuals who have claimed intolerance to Olean. The data suggest that subjects who previously experienced symptoms that they attributed to consuming products made with Olean may have mistakenly attributed their symptoms to these products.

Adolescent↗
PubMed1988

Prevalence of trichinosis in Canadian swine determined serologically by enzyme-linked immunosorbent assay.

Fifteen thousand three hundred and eighteen porcine sera from all regions of Canada were examined for the presence of anti-Trichinella antibodies using the enzyme-linked immunosorbent assay with an excretory-secretory antigen. Four sera (0.026%) revealed the presence of anti-Trichinella antibodies, with titers (optical density readings) that fell in the low positive or high negative range on repeated examinations. One animal originated in British Columbia and three in Ontario. Serological examination of swine in the herds at time of traceback did not reveal further animals with anti-Trichinella antibodies.

Animals↗
PubMed1987

On the explanation of the acidic pH requirement for in vitro activity of colicin E1. Site-directed mutagenesis at Glu-468.

The in vitro acidic pH dependence of colicin E1 channel activity was investigated by directed mutagenesis of Glu-468 in the colicin E1 channel domain, a residue conserved in the sequences of the four channel-forming colicins examined so far. Mutations were made to the amino acids leucine, serine, glutamine, or lysine, residues of different polarity and charge. All of the mutant polypeptides possessed high cytotoxic activity in vivo, although in vitro activity, especially with planar membranes, was lower than that of the wild type protein. A change in the in vitro acidic pH dependence of activity could be readily detected in the mutation to the hydrophobic leucine residue. The dependence of mutant activity on pH in the interval 3.5-5.0 was markedly smaller than that of the wild type, whether assayed on membrane vesicles or membrane bilayers. Differences in pH dependence between the wild type and the polar serine and glutamine mutants were small or of marginal statistical significance. No change in pH dependence could be detected with the charged lysine mutant. The residual pH dependence in all cases indicated that more than one carboxylic residue must be protonated to account for the increased activity at acidic pH values. A role of Glu-468 in the mechanism of channel formation or function was implied by the changes determined in vitro of channel parameters relative to the wild type: (i) the relatively small rates of current increase measured for colicin COOH-terminal peptide derived from the mutants, (ii) the small values of steady-state conductance of mutant peptide at pH 3.5, and (iii) the reduced anion selectivity of peptide from the serine mutant.

Amino Acid Sequence↗
PubMed1986

Chemical modification of the two histidine and single cysteine residues in the channel-forming domain of colicin E1.

The two histidine residues of COOH-terminal channel-forming peptides of colicin E1 were modified by addition of a carbethoxy group through pretreatment with diethylpyrocarbonate. The consequences of the modification were examined by the action of the altered product on both phospholipid vesicles and planar membranes. At pH 6, where activity is low, histidine modification resulted in a decrease of the single channel conductance from 20 pS to approximately 9 pS and a decrease in the selectivity for sodium relative to chloride, showing that histidine modification affected the permeability properties of the channel. At pH 4, where activity is high, the single channel conductance and ion selectivity were not significantly altered by histidine modification. The histidine modification assayed at pH 4 resulted in a threefold increase in the rate of Cl- efflux from asolectin vesicles, and a similar increase in conductance assayed with planar membranes. This conductance increase was inferred to arise from an increase in the fraction of bound histidine-modified colicin molecules forming channels at pH 4, since the increase in activity was not due to an increase in binding of the modified peptide, a change in ion selectivity, a change of single channel conductance, or a change in the pH dependence of binding. The sole cysteine in the colicin molecule was modified in 6 M urea with 5,5'-dithiobis(2-nitrobenzoic acid). The activities of the colicin and its COOH-terminal tryptic peptide were found to be unaffected by cysteine modification, arguing against a role of (-SH) groups in protein insertion and/or channel formation.

Amino Acid Sequence↗
PubMed1985

Localization of the immunity protein-reactive domain in unmodified and chemically modified COOH-terminal peptides of colicin E1.

The region of the colicin E1 polypeptide that interacts with immunity protein has been localized to a 168-residue COOH-terminal peptide. This is the length of a proteolytically generated peptide fragment of colicin E1 against which imm+ function can be demonstrated in osmotically shocked cells. The role of particular amino acids of the COOH-terminal peptide in the expression of the immune phenotype was studied. Chemical modification showed that the two histidine residues (His 427 and His 440) and the single cysteine residue (Cys 505) present in the COOH-terminal peptide were not necessary for the colicin-immunity protein interaction. The immunity protein was localized in the cytoplasmic membrane fraction, consistent with previous work of others on the colicin Ia immunity protein and the prediction from the immunity protein amino acid sequence that it is a hydrophobic protein. The distribution of hydrophobic residues along the immunity polypeptide was calculated.

Amino Acid Sequence↗
PubMed1984

Dependence of the activity of colicin E1 in artificial membrane vesicles on pH, membrane potential, and vesicle size.

The dependence on pH and membrane potential of the ability of colicin E1 and a COOH-terminal tryptic fragment of the colicin to form membrane channels has been measured using a chloride-sensitive electrode to measure colicin-induced ion efflux from asolectin vesicles of two different size classes. This method allows measurement of ion efflux on a faster time scale, with half-times for efflux less than or equal to 3 s, than previously possible using labeled solutes. Activity measurements were also made through the use of potential-indicating fluorescence probes. The activities of both colicin E1 and the fragment increased with decreasing pH. The activity of the colicin was maximum at pH values near 4.0, with an apparent pK of 4.5-4.6, whereas that of the COOH-terminal fragment continued to increase to the lowest pH value, 3.4, that could be used, showing an apparent pK less than or equal to 3.8. Using relatively small vesicles (average diameter approximately equal to 0.1 micron) made by a freeze-thaw procedure, chloride efflux caused by addition of fragment or colicin was independent of the initial transmembrane K+-diffusion potential imposed upon the system. However, with larger (0.5-micron diameter) vesicles prepared by a fusion method, the chloride efflux showed a dependence upon membrane potential, with the activity decreasing as the membrane potential was made more positive. The average size of the different vesicle populations was determined by electron microscopy. It is proposed that the lack of potential dependence observed in the freeze-thaw vesicles and the small voltage dependence, relative to planar membranes, seen in the larger fused vesicles, results from rapid discharge of the membrane potential and internal ion content of the vesicles.

Amino Acid Sequence↗