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J W Payne

Publications and source records attributed to J W Payne.

At least 19 recordsLinked to original sources
PubMed1992

Expression of periplasmic binding proteins for peptide transport is subject to negative regulation by phosphate limitation in Escherichia coli.

It is well recognised that phosphate limitation in Escherichia coli causes enhanced synthesis of a variety of proteins involved in maximising the uptake and utilisation of the available phosphate. In contrast to this situation, we report here that these same conditions repress synthesis of the periplasmic binding proteins for both the oligopeptide (Opp) and dipeptide permeases (Dpp), and of certain other periplasmic proteins. Regulation in the former case is mediated by the Pho regulon; genes controlled by this mechanism lack efficient -35 promoter regions, and instead, an activator protein, PhoB, binds to a specific 'Pho box' sequence, ten bases upstream from a -10 promoter, thereby facilitating binding of RNA polymerase and leading to enhanced transcription. In the latter case, putative Pho boxes can be identified in the promoter regions of opp and dpp (and of other binding proteins), but in these genes they overlap the RNA polymerase binding sites of good promoters. We speculate that this different Pho box location may allow PhoB to act as a repressor of transcription of these genes. The promoter region for the sigma factor, sigma 32, (RpoH) also contains a putative Pho box, implying that it may be involved in the enhanced synthesis and secretion of proteins required under phosphate limitation.

Alkaline Phosphatase↗
PubMed1992

The sequestration of [3H]spiperone by lymphocytes in schizophrenics and their first-degree relatives: a limited vulnerability marker?

The sequestration of [3H]spiperone by lymphocytes was studied in preserved cells obtained from 22 schizophrenic subjects and 40 of their relatives, and the results were compared with those obtained from 25 healthy control subjects. Mean displaceable sequestration values, obtained from measurements made at a single radioligand concentration (1nM) which optimised the relative contribution of "high affinity" sequestration, were found to be similar for all groups of subjects. Furthermore, displaceable spiperone sequestration was abnormally high in only a small proportion of the schizophrenics (13.6%) and their relatives (5%). There was no evidence that either exposure to neuroleptic medication or duration of illness had an effect on sequestration values. The results suggest that, at least until the required experimental conditions are better established, [3H]spiperone sequestration by lymphocytes does not offer a useful vulnerability marker for schizophrenia.

Adolescent↗
PubMed1991

Evaluation of the dipeptide and oligopeptide permeases of Candida albicans as uptake routes for synthetic anticandidal agents.

In order to obtain information essential for the design of synthetic anticandidal drugs that can exploit peptide permeases to gain access to intracellular targets, the substrate specificities of the dipeptide permease (Dpp) and oligopeptide permease (Opp) of Candida albicans have been studied. The permeases show strict stereospecificity, a preference for large, hydrophobic and N-terminal Ala residues, and marked discrimination against basic and acidic side chain residues. Comparison of results from several transport assays indicated that measuring loss of peptide substrate from the medium using fluorescence labelling procedures gave reliable transport rates and kinetic parameters, whereas in contrast, measuring accumulation of radioactivity from labelled substrates gave erroneous results arising from substrate metabolism and exodus. Intact accumulation of peptidase-resistant substrate against a concentration gradient was demonstrated. From amongst a variety of protein reagents tested, selective inhibition of dipeptide transport and presumed labelling of essential carboxyl group(s) in Dpp proteins was demonstrated using Woodward's reagent K.

Antifungal Agents↗
PubMed1991

Peptide substrates rapidly modulate expression of dipeptide and oligopeptide permeases in Candida albicans.

Previous studies showed that peptide transport activity in Candida albicans was completely repressed by NH4+, and that growth on amino acids as sole nitrogen source stimulated transport to a basal level. Here we show that addition of peptide mixtures to culture media gives a further 5-fold increase in transport of dipeptides and oligopeptides; the effect is specific for peptide transport, amino acid uptake being unaffected. Presence of peptides but not amino acids overrides NH4+ repression of peptide transport. Step-up activation of transport activity, caused by addition of peptides to incubation media, and step-down inhibition that accompanies removal of peptides, occurs rapidly (within 30 min at 28 degrees C). Step-up is independent of de novo protein synthesis. This substrate-induced regulation is compatible with a rapid, reversible activation of plasma membrane-bound peptide permease(s), or a mechanism of endocytosis involving a cycle of insertion and retrieval of preformed permease components. These results are considered in relation to the expression of peptide permeases in vivo, and the development of synthetic anticandidal peptide carrier prodrugs designed to exploit these systems.

Ammonia↗
PubMed1990

Simultaneous exploitation of different peptide permeases by combinations of synthetic peptide smugglins can lead to enhanced antibacterial activity.

Various synthetic, peptide prodrugs (smugglins) were tested alone and in combination for activity against Escherichia coli. The smugglins may be transported through any of three peptide permeases, and once inside the bacteria are activated by intracellular peptidase action to release their intrinsically impermeant, antibacterial moieties. When each such antibiotic peptide present in a mixture was accumulated via a different permease, synergistic effects could be observed. Synergy was also found when smugglins were combined with other non-peptide antibiotics. The principle of using smugglin combinations could extend the scope of their application, and should minimise the potential problem that can arise from the occurrence of resistant, transport mutants. The smugglin interactions were studied using a modified microtitre plate assay.

Anti-Bacterial Agents↗
PubMed1987

Intraocular lens power calculations. A practical evaluation in normal subjects at the Wilmer Institute.

The practical value of preoperative intraocular lens power calculations in "normal" eyes with less than 4.50 diopters (D) of myopia or hyperopia was evaluated in a consecutive series of 520 eyes that underwent cataract extraction and lens implantation by four experienced surgeons at The Wilmer Ophthalmological Institute. The observed postoperative results with the lenses selected by the surgeons were compared with results calculated for the measurement-predicted emmetropic power lens and for a standard 20-D lens. The need for postoperative spectacle correction of residual refractive errors was comparable for all three choices of lens. Only two eyes (0.4%) would have developed greater than 4.00 D of refractive error with either the "implanted" or "predicted-emmetropic" lenses, as would 11 eyes (2.1%) with the "standard" 20-D lens. The surgeons' deviation from the calculated emmetropic lens did not reduce postoperative refractive error.

Aged↗
PubMed1987

Clinicopathologic study of eyes obtained postmortem from a patient 6 and 2 years after operative choroidal hemorrhage.

We present the clinicopathologic features of a patient who developed bilateral choroidal hemorrhage during cataract surgery and who regained 20/30+ vision in each eye. Consequences related to the operative procedure and choroidal hemorrhage included iris and vitreous incarceration with inferior peripheral tractional retinoschisis, retained lens cortex, and an anterior capsule fragment lodged in the anterior chamber angle. A recent choroidal hemorrhage associated with a thrombosed vortex vein was observed in one eye. The favorable outcome was likely due both to preplaced sutures that allowed immediate tamponade of the hemorrhage and to the additional possible tamponading effect of an intact posterior capsule in the left eye. The possible role of venous stasis leading to vortex vein thrombosis as a cause of recent choroidal hemorrhage is discussed.

Aged↗
PubMed1986

Drug delivery systems: optimising the structure of peptide carriers for synthetic antimicrobial drugs.

This paper discusses the concept of smugglins, i.e., molecules that are formed by attaching to, or incorporating into, normal cell nutrients varied moieties as a means of transporting otherwise impermeant substances into cells. Examples of antimicrobial smugglins that use this principle in Nature are described. The rationally designed antibiotic smugglins investigated to date are critically reviewed. Criteria for the design of optimal peptide carriers for antimicrobial smugglins are considered. A computer-linked, continuous-flow system for rapid measurement of the kinetic parameters for substrate transport via peptide permeases is described which, together with current molecular, genetic and biochemical techniques, now provides the means to obtain the information on which rational design should be based; examples are given for Escherichia coli and Candida albicans. After an uncertain commercial start, it now seems likely that increasing understanding of the uptake processes and other relevant features will make drug targeting using peptide carriers an achievable goal. Certainly their widespread occurrence in Nature should provide added incentive for the design of synthetic smugglins.

Animals↗
PubMed1979

Direct determination of the properties of peptide transport systems in Escherichia coli, using a fluorescent-labeling procedure.

A direct study of peptide uptake by Escherichia coli was made using a fluorescent procedure. After incubation with the bacteria, peptides remaining in the medium were dansylated, separated chromatographically, and quantitated from their fluorescent intensities and/or from their incorporated radioactivity when tritiated dansyl derivatives were prepared. Peptide uptake was apparently not regulated and proceeded continuously until complete, with the absorbed peptides undergoing rapid intracellular hydrolysis and the excess amino acid residues leaving the cell. Thus, peptide uptake and amino acid exodus occur concurrently. However, peptidase-resistant substrates, e.g. triornithine and glycylsarcosine, which can be similarly estimated in cell extracts, were accumulated about 1,000-fold. The influence of amino acid composition and chain length on rates of transport was assessed. Different strains of E. coli showed variability in their rates of di- and oligopeptide transport. With respect to energy coupling, both the di- and oligopeptide permeases behaved like shock-sensitive transport systems.

Amino Acids↗
PubMed1977

Transport and hydrolysis of peptides by microorganisms.

The structural specificities of the dipeptide and oligopeptide permeases of E. coli are briefly reviewed and related to the requirements found for other microorganisms. New, quick, sensitive methods for studying peptide transport are described, based on the following: (i) peptide-dependent incorporation of free radioactive amino acid into newly synthesized protein by a double amino acid auxotroph, (ii) colorimetric assay of peptide-dependent enzyme synthesis by an amino acid auxotroph, (iii) dansyl fingerprint technique. These approaches provide information on peptide binding affinity to a permease and rates of peptide uptake and amino acid efflux. Among current and future research areas considered are: the influence of the pKb of the N-terminal amino group on transport, generality of peptide transport in microorganisms, energy coupling and regulation, involvement of binding proteins, and the 'smugglin' concept. Peptide hydrolysis, and nutritional ultilization of peptides, by microorganisms are briefly discussed.

Bacteria↗
PubMed1977

Monitoring enzyme synthesis as a means of studying peptide transport and utilization in Escherichia coli.

A new method has been developed for measuring peptide transport in aminoacid auxotrophs of Escherichia coli by following induction of beta-galactosidase. Appearance of the enzyme was determined after addition of inducer and peptides to amino-acid starved bacteria. For a given number of lysine equivalents, the rate and the extent of enzyme synthesis were the same for lysine and lysyl peptides; similar results were found for glycine and glycl peptides. Saturation constants for peptide transport were determined from the exogenous peptide concentration that gave half maximal rates of enzyme synthesis. The saturation constants, studies with mutants defective in peptide transport, and detection of competition between peptides for uptake, all endorsed earlier conclusions from growth tests about the structural specificities for peptide transport. The new method is quicker, more sensitive and more informative than growth tests.

Biological Transport↗
PubMed1975

Evidence for active transport of tripeptides by hamster jejunum in vitro.

1. This paper describes the uptake by rings of everted hamster jejunum in vitro of three peptides with structural features making them resistant to hydrolysis, glycylsarcosylsarcosine, glycylsarcosylsarcosylsarcosine and beta-alanylglycylglycine. 2. Glycylsarcosylsarcosine was taken up by a saturable mechanism and accumulated intact in the intracellular compartment of the intestinal wall, apparently against an electrochemical gradient. Its uptake was reduced by Na+-replacement, anoxia and metabolic inhibitors. It was concluded that uptake of this peptide was the result of Na+-dependent active transport. 3. Glycylsarcosylsarcosylsarcosine was very poorly taken up and its uptake did not appear to be the result of active transport. 4. Beta-Alanylglycylglycine appeared intact in the intracellular compartment of the intestinal wall on a substantial scale though it was not concentrated. No satisfactory evidence of uptake by a saturable mechanism was obtained. Uptake was, however, inhibited by anoxia, 2,4-dinitrophenol and Na+-replacement. Reasons are given for supposing that uptake of this peptide may be the result of Na+-dependent active transport by the same carrier as that utilized by glycylsarcosylsarcosine. 5. The results suggest that provided that they escape brush-border hydrolysis, tripeptides, like dipeptides, are actively transported into the absorptive cells of the intestinal mucosa, but that the ability of these cells to take up peptides by an active mechanism is unlikely to extend to tetrapeptides.

Alanine↗
PubMed1975

A common mechanism for transport of di- and tri-peptides by hamster jejunum in vitro.

1. This paper describes the results of a survey of the effects of peptides and amino acids on uptake by rings of everted hamster jejunum in vitro of glycylsarcosylsarcosine, a tripeptide which is taken up by an active mechanism but is very resistant to hydrolysis, appearing intact in the rings. The results of a small number of similar experiments with beta-alanylglycylglycine, another tripeptide which is taken up with very little hydrolysis, are also described. 2. Uptake of the two tripeptides was inhibited by other di- and tri-peptides, but not by free amino acids. The results suggest that dipeptides and tripeptides share a common uptake mechanism. The tetrapeptide glycylsarcosylsarcosylsarcosine did not inhibit uptake of glycylsarcosylsarcosine, and appears to be unable to utilize the uptake mechanism. 3. The results add to information about the influence of molecular structure on intestinal uptake of peptides by the system used by glycylsarcosylsarcosine, which is shared by a wide range of other di- and tri-peptides. In conjunction with previous results, they suggest that substitution of the N-terminal amino or C-terminal carboxyl groups reduces affinity for transport, that the presence of a beta-amino acid residue in a peptide is tolerated by the transport system, and that the presence of a D-amino acid residue reduces affinity for transport. Some peptides containing or made up of basic or acidic amino acid residues appear to have a low affinity for the transport system used by glycylsarcosylsarcosine. 4. Of two biologically active peptides, one, cephalexin, a peptide antibiotic, inhibited uptake of glycylsarcosylsarcosine and is probably transported by the same system. The other, prolylleucylglycineamide, which has the action of a hypothalamic regulatory factor, did not, and its structural features may make it unsuitable for carrier-mediated transport by the small intestine.

Animals↗