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Most artificial sweeteners have been determined by high-performance liquid chromatography, but not cyclamate. We propose a simple method using standard equipment without any chemical reaction involving the cyclamate ion by applying the technique of indirect photometry. Saccharin, dulcin and aspartame may also be determined, if present.
The refolding and reassembly of an integral membrane protein OmpF porin denatured in sodium dodecylsulfate (SDS) into its stable species by the addition of n-octyl-beta-D-glucopyranoside (OG) have been studied by means of circular dichroism (CD) spectroscopy and low-angle laser light scattering photometry coupled with high-performance gel chromatography. The minimal concentration where change in the secondary structure was induced by the addition of OG was found to be 6.0 mg/ml in CD experiments. A species unfolded further than the SDS-denatured form of this protein was observed at an early stage (5-15 min) of refolding just above the minimal OG concentration. In addition, the CD spectrum of protein species obtained above the minimal OG concentration showed that the protein is composed of a beta-structure which is different from the native structure of this protein. In light scattering experiments, no changes in molecular assemblies were observed when the OG concentration was below its minimal refolding concentration determined by CD measurements. Above the minimal concentration, a compact monomeric species was observed when denatured OmpF porin was incubated for 5 min at 25 degrees C in a refolding medium containing 1 mg/ml SDS and 7 mg/ml OG, and then injected into columns equilibrated with the refolding medium. After an incubation of 24 h before injection into the columns, predominant dimerization of this protein was observed in addition to incorrect aggregation.
The reversed-phase high-performance liquid chromatographic method employing photometry and fluorescence detection is described for the precise reproducible simultaneous measurement of total homocysteine (tHcy), cysteine (Cys), and glutathione (GSH) in human blood. Sample preparation involves conversion of disulfides to free thiols with triphenylphosphine, precipitation of proteins with trichloroacetic acid, conjugation of the thiols with monobromobimane (mBrB). The aminothiol assay is optimized by reduction and derivatization step conditions (pH, temperature and time of reactions) to obtain reliable quantitative results within the concentration range corresponding to normal and pathological levels of these thiols in human blood.
Macular pigment (MP) distribution profiles were measured for 18 subjects using a Moreland anomaloscope modified for motion photometry. The total amount of MP within the central 7 degrees was estimated from the distribution profile by numerical integration. Fundus autofluorescence images were obtained for eight of these subjects using a scanning laser ophthalmoscope. Peak optical density of MP increased with the total amount present, but the correlation was weakened by inter-subject differences in MP distribution. The mean MP distribution derived from mean grey-scale profiles of fundus autofluorescence images correlated closely with that obtained psychophysically (r=0.96). Autofluorescence imaging provides a fast non-invasive method for assessing MP in vivo.
PURPOSE: Laser flare photometry (LFP) is a new quantitative method for the evaluation of aqueous flare, making flare the only inflammatory parameter that can be evaluated precisely and objectively. The aim of this study was to characterize the inflammatory pattern of acute human leukocyte antigen-B27 (HLA-B27)-related anterior uveitis and to determine further clinical use and limitations of LFP in posterior inflammation. METHODS: In the first part of the study, 78 episodes of HLA-B27-related acute anterior uveitis were analyzed to determine mean pretreatment (initial) flare, mean flare evolution, need for additional periocular steroids, and mean duration of an episode. In the second part of the study, the use of LFP was further tested in posterior inflammation, first by analyzing the predictive value of a subclinical LFP-detected flare increase for disease recrudescence in posterior scleritis, and then by exploring clinical applications for LFP in posterior uveitis, where LFP was essential either in the establishment of a diagnosis or in guiding therapeutic decisions. RESULTS: Mean initial flare in HLA-B27-related acute anterior uveitis was 160 +/- 22 photons/msec, and mean duration of an episode was 18.5 +/- 15 days. A 50% and 90% flare reduction occurred after 2 and 8 days, respectively. In posterior scleritis, LFP was accurate in monitoring response to systemic steroid therapy and a small flare increase was predictive for disease recrudescence in five of six cases (predictive value 0.83, sensitivity 100%). In posterior uveitis, LFP was sensitive to monitor systemic treatments and to establish a diagnosis in unclear cases by measuring the effect of a selective therapy (therapeutic trial) on the flare level. CONCLUSION: In acute anterior HLA-B27-associated uveitis, LFP represented a potential improvement in management by allowing precise adjustment of therapy. In uveitis of the posterior segment, our data confirm the validity of LFP to monitor response and adjust systemic therapy and to detect disease recurrence in patients with a sufficient pretreatment level of associated blood-aqueous barrier disruption (flare).
Macaque monkeys are widely used as a model species for investigations of the biology of human vision. Previous measurements suggest that the cone-based spectral sensitivity of these two primates is greatly similar, but perhaps not identical. We measured the photopic spectral sensitivity of 42 male macaque monkeys from two species (Macaca mulatta, M. fascicularis) using an objective index, electroretinogram flicker photometry. The variations among individuals and between the two species were very small and there was no evidence for any significant cone pigment polymorphism in this sample. There are small but systematic differences in spectral sensitivity between macaque monkeys and equivalently tested human subjects--the monkeys were slightly more sensitive to short wavelengths (< 520 nm) and slightly less sensitive to wavelengths longer than this value. The results obtained from the curve fitting of standard photopigment absorption spectra to the spectral-sensitivity functions suggest that the difference between human and macaque monkey spectral sensitivity principally reflects differences in the relative proportions of the long- and middle-wavelength cones in the retinas of the two species.
The objective of the present work was to determine the interaction of cone inputs in the response of horizontal cells using heterochromatic flicker photometry (HFP). Intracellular electrophysiological recordings were made in horizontal cells of isolated retinae of carp maintained in physiological solution, with the receptor side up. Sharp glass microelectrodes filled with 3 M KCl solution with resistances between 100 and 120 M Omega were used. Stimuli comprised six cycles of two 6-Hz sinusoidal light waves in counterphase adjusted for the same number of quanta: a green light (550 nm) from a monochromator with a Xenon lamp and an LED red light (628 nm). The stimulation program consisted of 10 steps with the 550-nm wave at constant amplitude, while the 628-nm wave varied in increments of 10% up to 100%, followed by another 10 steps with the 628-nm wave at constant amplitude while the 550-nm wave varied in increments of 10% up to 100%. We recorded responses from four different horizontal cell classes: H1 (monophasic, broadband, n = 37), H2 (biphasic, red-green color-opponent, n = 13), and H3 (biphasic, blue-yellow color-opponent, n = 2) cone horizontal cells; and RH (monophasic, broadband, n = 3) rod horizontal cells. H1 and RH horizontal cells showed a similar cancellation point at a heterochromatic mixture consistent with mixed inputs from 630- and 550-nm cones. No cancellation point was found for the H2 cell class. Fish H1 cells add cone inputs and signal "luminance" in light levels appropriate for cone stimulation. The same occurs with RH cells, which also signal "luminance," but in light levels appropriate for rod work. For both cell classes there is an HFP cancellation point occurring at a combination of 628-nm and 550-nm lights in opposing phase that leads to the cancellation of the cell's response. No cancellation was found for H2 and H3 cells, which are the chromatically opponent horizontal cells in lower vertebrates.
Null measurements given by cancelling forces, voltages, or whatever, are used in physics for gaining 'objectivity'--by avoiding 'subjective' perceptions; but, somewhat paradoxically, null methods can be useful for studying perception itself. Here we consider cancelling opposed movements for photometry with coloured lights, and some recent experiments, carried out with John Harris, on nulling 'real' against opposed 'apparent' motion for teasing out some neural movement channels.
Two different commercially available urine dipsticks were evaluated to determine their usefulness as a screening test for the detection of non-infected urine specimens. The reactions of both dipstick strips were read visually and, in addition, one was read by semi-automated reflectance photometry. 2928 consecutive routine urine specimens received by the microbiology laboratory during normal working hours underwent testing by the conventional method of microscopy and culture and the results were compared with those obtained by dipstick testing. There were poor correlations between microscopy for red and white blood cells and dipstick results for blood and leucocyte esterase respectively. The dipsticks had a low positive predictive value (PPV) in identifying infected urines. In contrast, dipsticks had a very high negative predictive value (NPV) of 98.6-99.5% and correctly identified a significant proportion (about 1/3) of non-infected urines as reported by the conventional method. Introduction of dipstick testing of urine specimens in our hospital has led to significant time saving as dipstick-negative urines are not processed further (except for specific clinical indications) and there has also been a significant decrease (25%) in the number of specimens submitted to the laboratory. Further efficiencies may be obtainable with increased automation.
The first comprehensive sky survey of the extreme ultraviolet (EUV) spectral range performed by the Extreme Ultraviolet Explorer (EUVE) has uncovered a handful of very bright sources at wavelengths longer than the He I 504 angstroms photoionization edge. Among these objects are four white dwarfs with exceptionally low interstellar medium (ISM) column densities along the line of sight. Analysis of EUV photometry of the He-rich DO white dwarf MCT 0501-2858 and the H-rich DA white dwarf MCT 0455-2812 along one line of sight and of the DA white dwarfs HZ 43 and GD 153 near the north Galactic pole indicates that the overall minimum column density of the neutral material centered on the Sun is N(H I)= 0.5-1.0 x 10(18) cm-2. In the case of MCT 0501-2858, EUV photometric measurements provide a clear constraint to the effective temperature (60,000-70,000 K). Given these neutral hydrogen columns, the actual contribution to the density of neutral species from the immediate solar environment (the "local fluff") would only cover a distance of approximately 2-3 pc (assuming an average density n(H I) = 0.1 cm-3) leaving these lines of sight almost entirely within the hot phase of the ISM. A preliminary examination of the complete EUVE long-wavelength survey indicates that these lines of sight are exceptional and set a minimum column density in the solar environment.
Urine screening for bacteriuria by light-scatter photometry (Autobac) was evaluated for accuracy and compared with a colony count by the calibrated loop method. Incubation time, inoculum size, precision, and interference of particulate matter were evaluated in an effort to standardize the screening procedure. Results showed that urines could be accurately screened for Enterobacteriaceae by inoculating a single Autobac cuvette chamber with 0.1 or 0.2 ml of urine and determining the voltage change after four hours. A change of greater than or equal to 0.2 units indicates significant bacteriuria. Decreased accuracy was noted for urines having greater than 10(5) cfu/ml of Pseudomonas species or gram-positive cocci, possibly because these organisms grow more slowly.
Aberration in the physical structure or alignment of the eyes may produce pathologic neurocompensatory changes in the brain that, if left unattended, become irreversible. Two common examples of this abnormal state are accommodative esotropia and amblyopia. Both have a large optic component in their etiology and in most cases are correctable by optic methods. Generated retinal reflex photometry is a screening method that can detect, in the eyes of children, optic defects that tend to be the antecedents of more serious neurocompensatory processes. Detection at an early age permits more effective management and treatment of amblyopia. This technique is fast, safe, and inexpensive and provides a permanent record. It requires no response from the subject except a modicum of cooperation. It is attractive as an ocular screening method because it does not require highly trained personnel to administer the examination, yet appears to be accurate. The results lend themselves to mechanized processing.
The transepidermal water loss (TWL), photoelectric plethysmography and reflex photometry were parallelly registered on the involved hands and forearms of psoriatics. The TWL values showed a fairly good correlation with the clinical course of the disease: they increased during the active phase and decreased after return to normal. The vascular tests did not show a strict parallelism with the clinical state. On the basis of the findings, the temporal relations between epidermal and vascular factors during the different phases of the psoriatic process are discussed. The TWL can be used to predict a relapse occurring on the area investigated but not on a distant area.
A high resolution scanning microscope photometry system has been developed for use with standard G-banded chromosome preparations. Various alternative scanning methods and their limitations are reviewed. The computer algorithms which we use are described for the manipulation of the digitized image as produced by the microscope photometer; these include noise reduction and contrast enhancement as well as altering the orientation of the chromosome.
Additivity failures are common in heterochromatic photometry when the usual criterion of equal brightness is used. Using instead the criterion of a minimally distinct border between two precisely juxtaposed fields, we found that the additivity law holds.
A potential bioassay method for nystatin has been developed based on the ability of this antibiotic to bring out dose-related potassium ion efflux from susceptible cells of Saccharomyces cerevisiae, such extracellular potassium ion concentration being measured by flame photometry.
AIM: To investigate whether two methods of measuring macular pigment-namely, heterochromatic flicker photometry (HFP) and resonance Raman spectroscopy (RRS)--yield comparable data. METHODS: Macular pigment was measured using HFP and RRS in the right eye of 107 participants aged 20-79 years. Correlations between methods were sought and regression models generated. RRS was recorded as Raman counts and HFP as macular pigment optical density (MPOD). The average of the top three of five Raman counts was compared with MPOD obtained at 0.5 degrees eccentricity, and an integrated measure (spatial profile; MPODsp) computed from four stimulus sizes on HFP. RESULTS: The coefficient of variation was 12.0% for MPODsp and 13.5% for Raman counts. MPODsp exhibited significant correlations with Raman counts (r = 0.260, p = 0.012), whereas MPOD at 0.5 degrees did not correlate significantly (r = 0.163, p = 0.118). MPODsp was not significantly correlated with age (p = 0.062), whereas MPOD at 0.5 degrees was positively correlated (p = 0.011). Raman counts showed a significant decrease with age (p = 0.002) and were significantly lower when pupil size was smaller (p = 0.015). CONCLUSIONS: Despite a statistically significant correlation, the correlations were weak, with those in excess of 90% of the variance between MPODsp and Raman counts remaining unexplained, meriting further research.
The effect of magnesium sulphate in releasing calcium emission from interference by phosphate and sulphate has been investigated. Samples were diluted in 10 mM MgSO(4), 2 mM NaCl, giving final calcium concentrations of about 0.05 to 0.10 mM. In this diluent, galvanometer readings were proportional to calcium concentrations up to 0.4 mM. The magnesium sulphate released calcium emission from depression by phosphate and sulphate. The excess sodium chloride eliminated enhancement of calcium emission by added sodium and potassium in the sample. Subtraction of background readings excluded direct interference.A 3% correction was made for the effect of the viscosity of 1: 50 plasma dilutions. Satisfactory recoveries of added calcium were obtained from plasma, urine, and faeces using the diluent described above. Results on urine and faeces correlated closely with those obtained by an EDTA titration method. Results on plasma were consistently 2% higher by flame photometry than by EDTA titration. Other methods of calcium determination, depending on the use of radiation buffers or standard addition, were found to be unsatisfactory because of variable interference by phosphate at different calcium levels.