Conformational limitations of glycylsarcosine as a prototypic substrate for peptide transporters.

Peptide transporters are present in all species to absorb the small peptides that occur ubiquitously as products of proteolysis. The broad substrate specificities of these systems allow them to be exploited therapeutically for delivery of peptidomimetic drugs in microbes and man. To this end, glycylsarcosine is currently used as a standard substrate for assaying peptidomimetic transport by peptide transporters. However, in this study we find it is unsuitable as a general substrate, based on assays of its transport by model bacterial peptide transporters and computer-based conformational analysis of its structure. Of the two generic transporters for di- and tripeptides, exemplified by Dpp and Tpp in Escherichia coli, only Dpp can transport glycylsarcosine. The explanation for this finding came from molecular modelling, which indicated that glycylsarcosine can adopt only a restricted range of conformers compared with typical dipeptides, and that of the conformers with a trans peptide bond, the majority have the specific psi and phi backbone torsion angles needed for molecular recognition and transport by Dpp but none possessed psi and phi torsions required for recognition by Tpp; moreover, 38% of its conformers have cis peptide bonds that are not substrates for any peptide transporter. Thus, using glycylsarcosine as substrate in competition assays with compounds that typically form conformers recognised by both types of peptide transporter will underestimate their transport. These findings have implications for assays of oral availability of peptidomimetic drugs such as beta-lactams, ACE inhibitors and anti-viral compounds, for which glycylsarcosine is routinely used.

Autosomal dominant vitreoretinochoroidopathy. Report of the third family.

A family composed of 13 affected members in five generations (10 patients from four generations examined) had vitreal and ophthalmoscopic findings characteristic of autosomal dominant vitreoretinochoroidopathy, as described in two previous kindreds. Visual acuity was 20/25 or better in all but one patient. All affected individuals had vitreous liquefaction with or without peripheral vitreal condensations. Peripheral pigmentary changes and choroidal atrophy were characteristic. Six patients developed cataracts in their early 40s that required extraction. One patient had glaucoma, one developed a retinal detachment, and one had a spontaneous vitreous hemorrhage. Autosomal dominant vitreoretinochoroidopathy is a well-defined condition featuring presenile cataracts, vitreal degeneration, characteristic ophthalmoscopic findings, and good visual prognosis.

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.

Intraocular reticulum-cell sarcoma: clinico-pathologic study of four cases and review of the literature.

Four patients with primary intraocular reticulum-cell sarcoma were presented. All of the patients were followed at the Wilmer Institute for periods of up to ten years. All had decreased visual acuity and a uveitis that was refractory to standard forms of therapy. In one case, the correct diagnosis was made clinically. At autopsy, two of the patients had systemic reticulum-cell sarcoma, a third had intracranial reticulum-cell sarcoma, and in a fourth case the disease process was confined to the eye. The literature is reviewed and the clinico-pathologic features of the total of 14 cases are analyzed. It is emphasized that a recalcitrant uveitis was present in almost all of the cases reported. Differential diagnosis and methods of diagnosis are discussed.

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.

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.

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.

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.

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.

Substrate binding mutants of the higher plant ADP-glucose pyrophosphorylase.

To explore the structure-function relationships of the heterotetrameric higher plant ADP-glucose pyrophosphorylase, composed of a pair of large and small subunits, the small subunit cDNA was subjected to chemical mutagenesis and then co-expressed with the wild-type large subunit cDNA. Mutants were selected for their inability to complement a defective bacterial ADP-glucose pyrophosphorylase gene and, in turn, to accumulate glycogen as viewed by iodine staining of the cells. Based on these initial analyses, we subsequently identified four distinct classes of mutations which were glycogen-deficient but exhibited enzyme activity levels comparable to the normal recombinant enzyme under saturating reaction conditions. Three classes, each a product of single amino acid substitution, showed altered kinetic constants for substrates. Substitution of Asp252 to Asn conferred the enzyme lower affinity for glucose-1-phosphate, replacement of Asp121 to Asn resulted in an enzyme less responsive to both glucose-1-phosphate and ATP, while the Ala106 to Thr substituted enzyme contains altered sensitivity primarily to ATP. The fourth class, a Pro43 to Ser substitution, resulted in an enzyme with decreased sensitivity (8-fold) to the activator 3-PGA. Overall, the results of this study suggests that the two subunit types do not have identical roles in enzyme function and that the small subunit plays a more dominant role in catalysis than the large subunit.

Choice processing in emotionally difficult decisions.

Choice conflicts between one's important values may cause negative emotion. This article extends the standard effort-accuracy approach to explaining task influences on decision processing by arguing that coping goals will interact with effort minimization and accuracy maximization goals for negatively emotion-laden decision tasks. These coping goals may involve both a desire to process in a thorough, accurate manner and a desire to avoid particularly distressing aspects of processing. On the basis of this extended framework, the authors hypothesized and found in 3 experiments that decision processing under increasing negative emotion both becomes more extensive and proceeds more by focusing on one attribute at a time. In particular, increased negative emotion leads to more attribute-based processing at the beginning of the decision process. The results are inconsistent with views that negative emotion acts only as an incentive or only as a source of decision complexity.

Presence of distinct virtual backbone torsion angles in dipeptide conformers.

Zwitterionic dipeptides have recently been shown to exist in water mainly as nine conformational forms with specific combinations of backbone Psi, omega and Phi torsions, which allows conformer-specific molecular recognition of peptide ligands by proteins. Here, we show that pairs of virtual backbone torsions can also define these nine conformational forms, and that comparing these virtual torsions in dipeptides with those of backbone-modified pseudopeptides offers an improved procedure for evaluating peptidomimetics for therapeutic applications.

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.

Expulsive hemorrhage: its incidence in cataract surgery and a report of four bilateral cases.

Between 1978 and 1983, 13,890 cataract extractions were performed in Baltimore at JHH and the GBMC with 14 expulsive hemorrhages for an incidence of 0.10%. In the years 1963 through 1983, 180,690 cataract extractions were performed in Taxila, Pakistan with 87 expulsive hemorrhages for an incidence of 0.05%. Reasons for the significant differences in incidence are presented. The six reported cases of bilateral expulsive hemorrhage are reviewed. Four more cases are added. A classification of choroidal hemorrhage is presented.