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Biomedical subjects

G Kemp

Publications and source records attributed to G Kemp.

At least 19 recordsLinked to original sources
PubMed1992

A novel acetylcholine receptor-related peptide blocks canine cardiac ganglia and inhibits the nicotinic receptor of PC-12 cells.

A 13 amino acid peptide from the calf muscle acetylcholine receptor has been previously shown to bind both snake neurotoxins and acetylcholine. In the experiments reported here a modified complementary peptide (cAChR) derived from that acetylcholine receptor peptide was tested for biological activity in a canine heart preparation. It was expected that the modified complementary peptide would exhibit either acetylcholine-like effects or acetylcholine inhibiting effects, since, as a complementary peptide to the receptor, it should resemble acetylcholine. In these studies cAChR was administered via the sinus node artery of dog hearts in intact animals which were anesthetized with pentobarbital, intubated, and prepared with local cardiac electrograms and force gauges. cAChR was also injected directly into thoracic sympathetic ganglia. Both approaches demonstrated cAChR inhibition of neural transmission, cAChR was added to the medium of carbachol stimulated PC-12 cells. In these cells, derived from a rat pheochromocytoma, sodium flux is controlled by neural nicotinic receptors. With or without preincubation cAChR inhibited carbachol stimulation of sodium flux, exhibiting a Ki of approximately 9 x 10(-5) (similar to that of hexamethonium). Thus cAChR appears to be a novel synthetic peptide which interrupts nicotinic cholinergic neural transmission by acting as an antagonist of the neural nicotinic receptor.

Amino Acid Sequence↗
PubMed1992

Proteolysis is a key process in virus replication.

Proteases were amongst the first enzymes to be isolated and crystallized, and the discovery of their existence in viruses and the realization of the vital role they play has given a new lease of life to one of the oldest topics in biochemistry. Already we have seen the discovery of new variations on well-studied reaction mechanisms and there is the promise of others to come that may be totally novel. When this is allied to the prospect of developing the knowledge which is beginning to accrue into a much needed antiviral therapy, it is clear that viral proteases and their key role in viral replication will be an increasing focus of attention for some time to come.

Animals↗
PubMed1991

A total ban on workplace smoking is acceptable and effective.

The acceptability and effectiveness of a total workplace smoking ban in Telecom Australia was evaluated in a series of studies. Staff in a sample of representative areas were surveyed prior to the introduction of the bans, then 6 and 18 months afterward. By 18 months 81% of all staff, including 53% of smokers, approved of the bans. Sixty-six percent of staff reported a total ban was operative, and 31% reported a total ban except for a smoking room, leaving only 3% reporting lesser restrictions. Smokers were smoking between three and four less cigarettes per work day, and the numbers of smokers had decreased by about double the community rate. The policy had little perceived effect on productivity but resulted in some tension between staff that progressively decreased and now is limited to the few areas where there were problems with compliance. A subsample of managers and staff were interviewed and factors relevant to successful implementation of the policy were identified. These included a clear statement of policy, strong managerial support via equipping managers with leadership and negotiating skills, and the use of occupational health nurses. It is important to provide assistance to affected staff to help them adjust to the ban both before as well as in the months after implementation.

Adult↗
PubMed1989

A dye-photosensitized reaction that generates stable protein-protein crosslinks.

Irradiation of fibrinogen with visible light for 30 s in the presence of 1-1000 microM fluorescein was found to crosslink fibrinogen both inter- and intramolecularly. Optimum crosslinking was achieved at dye concentrations of around 100 microM and the amount of crosslinking was shown to increase with pH. Crosslinking was inhibited in the presence of 50 microM tryptophan or tyrosine and enhanced in the presence of 5 mM histidine. Twice as much crosslinking was found to take place under anaerobic conditions. These observations are consistent with a dye-photosensitized reaction following the hydrogen abstraction pathway. The subunits of eukaryotic ribosomes and those of phosphorylase a were also crosslinked by the method described.

Amino Acids↗
PubMed1989

The influence of calcium ions on fibrinogen conformation.

The conformation of fibrinogen has been examined using the techniques of dye-photosensitized surface labelling and cross-linking. The results obtained suggest that fibrinogen is a flexible molecule and its conformation is influenced by the concentration of calcium ions. These effects are mediated through binding to the low-affinity calcium binding sites of fibrinogen. In particular the C-terminal regions of the [A]alpha chain are more exposed at higher calcium concentrations creating a molecule which is more liable to form inter-molecular interactions.

Calcium↗
PubMed1989

The structures of human C1r and C1s and their relationship to other serine proteases.

The recent sequencing of the C1 subcomponents has allowed comparison with other molecules of homologous primary structure. Where tertiary structures are available for at least one member of the family it is possible to make further progress by modelling the amino acid sequence of the complement protein into the three-dimensional coordinates of the directly determined structure, thereby obtaining an approximation of the structure of the complement protein. Molecular modelling allows structure-function relationships to be explored and suggests further experiments that may be amenable to techniques such as site-directed mutagenesis.

Amino Acid Sequence↗
PubMed1988

Correction of high pelvic defects with the inferiorly based rectus abdominis myocutaneous flap.

The two inferiorly based rectus abdominis myocutaneous flaps are the most versatile and accessible flaps for high pelvic defects. Their primary contribution is in the obliteration of the pelvic "deadspace." At the present time, these useful flaps are generally considered only for massive defects of the perineum, groin, and pelvis, but improved flap designs will enhance their usefulness for smaller defects.

Female↗
PubMed1987

Cholinergic function and alpha-bungarotoxin binding in PC12 cells.

The cell line PC12, derived from an adrenal chromaffin cell tumor, expresses both ganglionic (C6) acetylcholine receptors (nAChR) and an alpha-bungarotoxin (BGT) binding protein of unknown function. We measured nicotinic Na+ fluxes of 180-260 nmol/mg protein X min and 0.35-0.8 pmol [125I]BGT binding sites/mg protein; 45-65% of the [125I]BGT binding was to intracellular sites. We blocked ganglionic Na+ fluxes with reversible and irreversible inhibitors and tested whether a residual BGT-sensitive flux could be identified. No such flux was detected. These experiments place an upper limit on the amount of an undetected Na+ flux such that we question whether the BGT binding protein could act as a functional nAChR X Na+ flux and [125I]BGT binding were irreversibly inactivated by the affinity-directed antagonist 4-(N-maleimido)benzyltrimethylammonium bromide (MBTA), and the appearance of new nAChRs and BGT binding proteins was monitored. New ganglionic nAChRs appeared at a rate of 0.029 hr-1, corresponding to a steady state turnover t1/2 of 24 hr. BGT binding protein was synthesized more rapidly (K = 0.11 hr-1, t1/2 = 6.5 hr). When protein synthesis was simultaneously blocked with cycloheximide, insertion of BGT binding protein into the plasma membrane decreased to 11% of control values. Cycloheximide also induced a biphasic decline in intracellular BGT binding sites. Incubation of PC12 cells in 5 mM carbamylcholine for varying intervals resulted in a rapid 30% loss of Na+ flux activity. In contrast, the concentration of BGT binding protein did not change.

Animals↗
PubMed1986

Ganglionic nAChRs and high-affinity nicotinic binding sites are not equivalent.

High-affinity (Kd approximately equal to 10 nM) binding sites for nicotine and acetylcholine (ACh) have recently been identified in vertebrate brain. It has been suggested that these sites are desensitized ganglionic (C6) nicotinic acetylcholine receptors (nAChRs). We have tested the pheochromocytoma cell line PC12, which is known to contain well-expressed C6 nAChRs, to determine if these nAChRs are associated with high-affinity [3H]ACh-binding sites. We found that the high-affinity nicotinic [3H]ACh-binding site is absent in PC12 cells. We also found that the concentration of nicotine or ACh necessary to desensitize carbamylcholine-stimulated Na+ flux was at least two orders of magnitude greater than the concentrations used in binding experiments. We conclude that high-affinity nicotinic binding sites are not equivalent to C6 ganglionic receptors.

Acetylcholine↗
PubMed1985

Purification and characterization of the alpha-bungarotoxin binding protein from rat brain.

The alpha-bungarotoxin (BGT) binding protein from rat brain has been purified and its polypeptide chain composition has been examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Polypeptide chains with Mrs of 55,000, 53,500 and 49,000 have been identified as constituents of the protein. The affinity ligand [3H]maleimidobenzyl trimethylammonium bromide ([3H]MBTA), used to identify the ligand binding site on neuromuscular junction acetylcholine receptors (NMJ AChRs), binds to the 55,000 dalton polypeptide chain. Using a technique where ligands are bound to the protein while the protein is immobilized on alpha-cobratoxin-Sepharose 4B, it was established that the brain BGT binding protein, like NMJ AChRs, possesses two binding sites for BGT. These experiments reinforce previous evidence that the brain BGT binding protein is closely related but not identical to NMJ AChRs.

Animals↗
PubMed1979

The presence of a Ca2+ bridge within the gamma chain of human fibrinogen.

The presence of Ca2+ increased the mobility of fragment D, and the gamma chain from fibrinogen on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate, suggesting that a Ca2+ was associated with these fibrinogen derivatives. The mobilities of the constituent chains from fragment D produced under various conditions, indicate that Ca2+ bound to fibrinogen form an intrachain bridge towards the C-terminus of each gamma chain.

Binding Sites↗
PubMed1978

Diuretics.

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Benzothiadiazines↗