Oligomerization of L-gamma-carboxyglutamic acid

Unlike glutamic acid, L-gamma-carboxyglutamic acid does not oligomerize efficiently when treated with carbonyldiimidazole in aqueous solution. However, divalent ions such as Mg2+ catalyze the reaction, and lead to the formation of oligomers in good yield. In the presence of hydroxylapatite, L-gamma-carboxyglutamic acid oligomerizes efficiently in a reaction that proceeds in the absence of divalent ions but is further catalyzed when they are present. After 'feeding' 50 times with activated amino acid in the presence of the Mg2+ ion, oligomers longer than the 20-mer could be detected. The effect of hydroxylapatite on peptide elongation is very sensitive to the nature of the activated amino acid and the acceptor peptide. Glutamic acid oligomerizes more efficiently than L-gamma-carboxyglutamic acid on hydroxylapatite and adds more efficiently to decaglutamic acid in solution. One might, therefore, expect that glutamic acid would add more efficiently than L-gamma-carboxyglutamic acid to decaglutamic acid on hydroxylapatite. The contrary is true--the addition of L-gamma-carboxyglutamic acid is substantially more efficient. This suggests that oligomerization on the surface of hydroxylapatite depends on the detailed match between the structure of the surface of the mineral and the structure of the oligomer.

Polymerization on the rocks: negatively-charged alpha-amino acids

Oligomers of the negatively-charged amino acids, glutamic acid, aspartic acid, and O-phospho-L-serine are adsorbed by hydroxylapatite and illite with affinities that increase with oligomer length. In the case of oligo-glutamic acids adsorbed on hydroxylapatite, addition of an extra residue results in an approximately four-fold increase in the strength of adsorption. Oligomers much longer than the 7-mer are retained tenaciously by the mineral. Repeated incubation of short oligo-glutamic acids adsorbed on hydroxylapatite or illite with activated monomer leads to the accumulation of oligomers at least 45 units long. The corresponding reactions of aspartic acid and O-phospho-L-serine on hydroxylapatite are less effective in generating long oligomers, while illite fails to accumulate substantial amounts of long oligomers of aspartic acid or of O-phospho-L-serine.

Retreatment for significant regression after excimer laser photorefractive keratectomy. A prospective, randomized, masked trial

PURPOSE

Regression, a gradual partial or complete return to the myopic state, remains a common complication of excimer laser photorefractive keratectomy (PRK) and limits the predictability of refractive outcome, especially in high myopia. An estimated 10% to 20% of patients, therefore, request a repeat PRK procedure. This study was designed to provide patient selection criteria and guidelines for successful retreatment.

METHODS

One hundred six patients who had regressed were randomized to 1 of 4 retreatment groups comprising (1) those with minimal haze after their first PRK who received an exact retreatment; (2) those with minimal haze treated with a 50% deliberate overcorrection; (3) those with significant haze (> or = 2+ haze) given an exact retreatment; and (4) those with significant haze who received a 50% overcorrection. A Visx 20/20 laser was used in each case. Mean follow-up after retreatment was 12 months (range, 6-18 months).

RESULTS

Deliberate overcorrection (groups 2 and 4) resulted in a statistically significantly better refractive outcome (P = 0.026 at 6 months). Analysis of variance showed that significant haze after the first PRK was the most important predictor of a poor outcome after retreatment, other factors being high original myopia, marked regression, and loss of best-corrected visual acuity.

CONCLUSIONS

A retreatment PRK procedure for significant regression will reduce residual myopia significantly in the majority of patients, and a deliberate overcorrection (50%) reduces the chance of further regression. However, patients with high myopia who have regressed beyond approximately -3.50 diopters originally and who show significant anterior stromal haze (> 2+) should be retreated only with great caution, because of the risk of further regression, haze, and loss of visual acuity.

Attendance of contact lens wearers at an ophthalmic accident and emergency unit

Contact lens (CL) complications account for 2.2-10.0% of patients attending ophthalmic Accident and Emergency (A&E) units. A survey was conducted to evaluate disease severity among CL wearers attending the Oxford Eye Hospital A&E Unit. CL wearers without a medical indication for CL wear completed a short questionnaire eliciting CL type and wear schedule. Subsequently, A&E Senior House Officers indicated the diagnosis and whether, in their opinion, the patient could have been managed by their optometrist or contact lens practitioner. Approximately half of the CL wearers (321/653, 49%) presented with CL related disorders, but only 16% (53/321) of these had potentially sight-threatening disease. More than a third of these patients were deemed to be inappropriately attending (125/321, 39%), presenting with minor problems such as corneal abrasions, CL handling difficulties and CL solution 'accidents'. Better patient instruction, together with encouragement to consult their optometrist or contact lens practitioner first if problems occur, would greatly reduce the burden of A&E attendance by CL wearers with minor complaints.

Bioluminescence: A Rapid Indicator of Escherichia Coli O157:H7 in Selected Yogurt and Cheese Varieties

Outbreaks of enterohemorrhagic Escherichia coli O157:H7 have been commonly associated with products derived from ground beef, but recently the organism has been implicated as the causative agent in outbreaks involving yogurt and cheese. This finding has raised concern about the potential for its growth and survival in fermented dairy products. A bioluminescent strain of E. coli O157:H7 was used to determine postprocessing survival in yogurt with live cultures at pH 4.17, 4.39, and 4.47 stored at 4 and 10°C. In addition, survival of E. coli O157:H7 was monitored during the manufacture of Cottage, Colby, Romano, and Feta cheeses. Results indicated survival for 8 and 5 days at 4 and 10°C respectively in yogurt at pH 4.17, 17 and 15 days at 4 and 10°C respectively in yogurt at pH 4.39, and 17days at both 4 and 10°C in yogurt at pH 4.47. E. coli O157:H7 did not survive cooking procedures at 56°C in Cottage cheese. However, the pathogen survived for 27, 30, and 27 days in Colby, Romano, and Feta cheeses respectively. A high correlation of r² > 0.89 was obtained between counts of bioluminescenct colonies and standard plate count for all yogurt and cheese varieties, indicating that bioluminescence was a sensitive and rapid indicator of cellular viability for E. coli O157:H7. Survival of the pathogen, as indicated by this method, is possible in highly acidic environments even at refrigeration temperatures. This poses a potential hazard should postprocessing contamination occur.

Oligomerization of negatively-charged amino acids by carbonyldiimidazole

The carbonyldiimidazole-induced oligomerizations of aspartic acid, glutamic acid and O-phospho-serine are amongst the most efficient reported syntheses of biopolymers in aqueous solution. The dependence of the yields of products on the concentrations of reagents, the temperature and the enantiomeric composition of the substrate amino acids are reported. Catalysis by metal ions, particularly by Mg2+, is described. These reactions do not generate significant amounts of material in the size-range of several tens of residues that are thought to be needed for a polymer to function as a genetic material.

Synthesis of long prebiotic oligomers on mineral surfaces

Most theories of the origin of biological organization assume that polymers with lengths in the range of 30-60 monomers are needed to make a genetic system viable. But it has not proved possible to synthesize plausibly prebiotic polymers this long by condensation in aqueous solution, because hydrolysis competes with polymerization. The potential of mineral surfaces to facilitate prebiotic polymerization was pointed out long ago. Here we describe a system that models prebiotic polymerization by the oligomerization of activated monomers--both nucleotides and amino acids. We find that whereas the reactions in solution produce only short oligomers (the longest typically being a 10-mer), the presence of mineral surfaces (montmorillonite for nucleotides, illite and hydroxylapatite for amino acids) induces the formation of oligomers up to 55 monomers long. These are formed by successive 'feedings' with the monomers; polymerization takes place on the mineral surfaces in a manner akin to solid-phase synthesis of biopolymers.

Catalysis of the oligomerization of O-phospho-serine, aspartic acid, or glutamic acid by cationic micelles

Treatment of relatively concentrated aqueous solutions of O-phospho-serine (50 mM), aspartic acid (100 mM) or glutamic acid (100 mM) with carbonyldiimidazole leads to the formation of an activated intermediate that oligomerizes efficiently. When the concentration of amino acid is reduced tenfold, few long oligomers can be detected. Positively-charged cetyltrimethyl ammonium bromide micelles concentrate the negatively-charged activated intermediates of the amino acids at their surfaces and catalyze efficient oligomerization even from dilute solutions.

Serum lactate dehydrogenase (LDH) in Pneumocystis carinii pneumonia, tuberculosis, and bacterial pneumonia

An increase in serum lactate dehydrogenase (LDH) activity is commonly taken to support the presumptive diagnosis of Pneumocystis carinii pneumonia (PCP), although the LDH level may also be increased in other lung infections and in a variety of extrapulmonary disorders. To assess its diagnostic value in patients with fever, lung infiltrates, and a high prevalence of HIV infection, we compared LDH levels in 42 hospitalized patients with PCP, 71 with disseminated tuberculosis (TB), 40 with pulmonary TB, and 37 with bacterial pneumonia. Peak LDH level was higher (p < 0.05) in patients with PCP (547 +/- 157 U/L) and disseminated TB (569 +/- 338 U/L) than in patients with pulmonary TB (258 +/- 66 U/L) or bacterial pneumonia (331 +/- 139 U/L). However, substantial overlap between groups limited its diagnostic value for individual patients. Expressing LDH as its ratio to simultaneous serum aminotransferases (AST or ALT) did not enhance its discriminatory value. Most patients in each group had abnormalities in other serum enzymes (AST, ALT, alkaline phosphatase, gamma-glutamyltransferase), making an isolated elevation of LDH level uncommon (21% of PCP cases). Serum LDH has a high sensitivity for PCP (100% in this series) but must be interpreted with caution given its lack of specificity.

Rapid changes in thyroid function tests upon treatment of tuberculosis

SETTING

Inpatient service and tuberculosis (TB) clinic of a public hospital.

OBJECTIVES

(1) To test the hypothesis that an hepatic effect of antituberculosis drugs increases serum thyroxine-binding globulin (TBG); (2) to resolve conflicting reports on thyroid function in TB.

DESIGN

Measurement of serum thyroid hormones, thyroid hormone binding (T3RU) and binding proteins (TBG, transthyretin [TTR] and albumin) in 38 patients with active TB and in 29 healthy tuberculin-positive controls, before and about 10 days into therapy.

RESULTS

With therapy of TB (with isoniazid [INH], rifampin [RIF], ethambutol and/or pyrazinamide), TBG increased above control values and T3RU decreased (P < 0.001). These changes were weakly correlated with liver enzyme activities but did not predict clinical hepatitis, which developed in only 1 patient. T3 was initially subnormal in 61% of 38 TB patients, while T4, thyrotropin (TSH) and TBG were normal. T3, TTR and albumin, all negative acute phase reactants, increased towards normal by day 10 (P < 0.001). Thyroid function remained unaltered in 14 control patients taking INH, whereas T3RU decreased (binding increased) and T3 increased in 15 taking INH and RIF (P < 0.001).

CONCLUSIONS

TB patients manifest the expected low T3 of non-thyroid illness, but, unlike most sick patients, usually have normal or increased serum binding of thyroid hormones. Chemotherapy further increases binding by increasing TBG, an effect probably due to RIF.

Chemical species in cheese and their origin in milk components

Cheese making is the process of concentrating milk fat and protein by separation from water and soluble components. The objective of the cheese maker is to maximize yield efficiency by optimum utilization of each milk component while not compromising cheese quality. Cheese yielding potential of milk may be increased by selective breeding for specific protein genotypes, especially the BB variant of both kappa-casein and beta-lactoglobulin. Milk fat is included in cheese by occlusion into the protein coagulum. Participation of casein in both lactic and rennet coagulation is nearly complete so that casein losses to the whey occur mainly during cutting and the early stages of cooking. In lactic cheese, excepting cottage cheese, it is possible to eliminate losses of fines by centrifugal or membrane separation of curd. In heat-acid precipitated varieties protein recovery is increased by inclusion of whey proteins but fat recovery is very dependent on coagulation conditions. In ripened cheese obtaining the correct basic structure and composition is critical to texture and flavour development during curing.

Transient exacerbation of tuberculous lymphadenitis during chemotherapy in patients with AIDS

We describe three men with disseminated, drug-sensitive tuberculosis and advanced human immunodeficiency virus disease (CD4+ lymphocyte count, < 50/mm3) who had flares of tuberculous lymphadenitis with suppuration during the initial weeks of successful chemotherapy. Bactericidal drugs may kindle these transient exacerbations, which involve neutrophils but apparently do not require normal helper T cell function. In patients with AIDS, as in immunocompetent individuals, treatment-related flares of lymphadenitis are usually not an adverse sign, provided that drug resistance and nonadherence have been excluded.

Effectiveness of unsupervised oculokinetic perimetry for detecting glaucomatous visual field defects

Oculokinetic perimetry (OKP) is a simple, inexpensive technique which was introduced primarily to promote more widespread use of visual field screening for glaucoma. The effectiveness of unsupervised OKP screening was evaluated using 145 non-glaucomatous patients and 64 patients with previously undiagnosed primary open angle glaucoma. Glaucoma cases were validated by the extended 132 point program on the Henson CFS2000 instrument. Both sample populations were representative of patients presenting for primary vision care. The effectiveness of the 26 point OKP test was compared with the 26 point Henson screening program. The results suggest that, in contrast to the Henson screening test (sensitivity = 85.1%, specificity = 93.8%), unsupervised OKP screening (sensitivity = 25.0%, specificity = 93.6%) has limited effectiveness for detecting glaucomatous visual field defects.

The limits of template-directed synthesis with nucleoside-5'-phosphoro(2-methyl)imidazolides

In earlier work we have shown that C-rich templates containing isolated A, T or G residues and short oligo(G) sequences can be copied effectively using nucleoside-5'-phosphoro(2-methyl)imidazolides as substrates. We now show that isolated A or T residues within an oligo(G) sequence are a complete block to copying and that an isolated C residue is copied inefficiently. Replication is possible only if there are two complementary oligonucleotides each of which acts as a template to facilitate the synthesis of the other. We emphasize the severity of the problems that need to be overcome to make possible non-enzymatic replication in homogeneous aqueous solution. We conclude that an efficient catalyst was involved in the origin of polynucleotide replication.

Reflectance pulse oximetry measurements from the retinal fundus

Conventional transmission pulse oximetry is a noninvasive technique for the continuous monitoring of arterial oxygen saturation (SaO2) from peripheral vascular beds such as the finger tip or earlobe. In this paper we propose to exploit the unique transparency of the ocular media to make reflectance pulse oximetry measurements on the retinal fundus. This technique potentially offers significant advantages over conventional pulse oximetry, primarily the ability to monitor cerebral, as opposed to peripheral, oxygen saturation. We have developed an in vitro system to stimulate the retinal circulation and ocular optics. This system consists of a flexible cuvette located in a model eye and an extracorporeal blood circuit to stimulate arterial blood flow. The system was used to investigate the relationship between SaO2 and the R/IR ratio in reflectance pulse oximetry. To enable in vivo measurements to be made, we also modified a standard haptic contact lens to hold the pulse oximeter probe in front of the pupil. In a preliminary study, the lens was fitted to an awake volunteer and cardiac-synchronous signals were detected by the retinal pulse oximeter.

Reliability of high- and low-contrast letter charts

The aim of this study was to measure the reliability, in test score units, of several clinical tests which use high- and low-contrast letters, and to provide an estimate of what constitutes a significant change in performance over time. Patients with normal vision and with early or subtle eye disease were recruited so that the results would be representative of the population likely to present for primary vision screening. Patients were tested on the Bailey-Lovie logMAR chart, the Regan low-contrast letter charts and the Pelli-Robson low-contrast letter chart on two occasions; the two test sessions were separated by at least four weeks to give an estimate of reliability appropriate for the conditions under which the tests are likely to be used. A 'significant change', i.e. one which would be observed in only about 5% of patients with stable visual performance, was about +/- 2 'steps' of the measurement scale, i.e. +/- 2 lines for the Bailey-Lovie and Regan charts and +/- 2 letter groups for the Pelli-Robson chart.

Evaluation of two infrared autorefractors in pseudophakia

We investigated the viability of using an objective infrared autorefractor to identify high corneal astigmatism (> 3.00 D) in a pseudophakic population. The eyes of 91 patients, who had recently undergone cataract extraction and intraocular lens implanation, were refracted manually and using two infrared autorefractors, a Canon RK-1 and a Nikon NR-2000. Autorefractor measurements were repeated to provide estimates of reliability for each instrument. LogMAR visual acuities were also recorded with both the manual and autorefractor corrections. Approximately 75% of repeat autorefractor measurements were within 0.50 D of the initial readings, and about 75% of measurements were within 1.00 D of the manual refractions. Visual acuities with manual corrections were, on average, one line better than with autorefractor corrections. By validating the autorefractors against manual refraction, the efficiency of the autorefractors for detecting astigmatism > 3.00 D was calculated. Setting the cut-off criterion to ensure high sensitivity (95%), so that almost all patients with > 3.00 D were detected, resulted in both instruments having a poor specificity of about 40%.