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A Balter

Publications and source records attributed to A Balter.

15 recordsLinked to original sources
PubMed1996

[Health risks in connection with fungi: a contribution to the assessment of fungi in the risk potential of safety provisions].

Fungi have been used for a long time in industrial production. Recent developments in biotechnology have lead to an increased awareness of possible health hazards connected with the use of microorganisms in industries. In order to avoid potential risks by appropriate protective measures it is necessary to assess the microorganisms, including fungi, with respect to their species-related risk potential. For this purpose, fungi were classified into three risk groups of which group I contains non-hazardous fungi and group III fungi with high risk. Most difficulties arise when it is to be decided if a fungus belongs to group I or group II which includes most pathogenic fungi. The present study was designed to provide data which facilitate the assessment of potentially hazardous fungi. It is based on the evaluation of the pertinent mycological literature as represented in the Review of Medical and Veterinary Mycology in the years from 1980 till 1989.

Biotechnology↗
PubMed1991

Some fluorescence properties of cataractous eye lenses.

The loss of transparency of the ocular lens is caused by the increase of light scattering as a result of structural changes and by the increased absorption of the visible light due to the accumulation of pigments. Following light absorption, these pigments undergo non-radiative and radiative (luminescence) processes which can be monitored spectroscopically. The paper presents some new results concerning the excitation spectra, decay times and polarization of the lenticular fluorescence. Fluorophore heterogeneity manifests itself in all the experimental data. A striking behaviour of the emission anisotropy as a function of temperature is found, particularly for cortical cataract lenses, indicating temperature-induced structural changes at about 20 degrees C.

Adolescent↗
PubMed1984

Antidepressant tachyphylaxis.

We report eleven patients in whom tachyphylaxis to antidepressants, lithium or ECT occurred. These cases are a small sample of patients we have encountered in whom an initial good response to mood regulating drugs was not sustained. We suspect that systematic studies would reveal that tachyphylaxis is a common phenomenon with antidepressant therapies.

Adult↗
PubMed1984

Cross-national reliability study of a schedule for assessing personality disorders.

The inter-rater reliability of a schedule used to assess personality disorders was examined. The Personality Assessment Schedule (PAS) involves an interview with both the patient and a close informant and the ratings for the informant are given most weight in the final scoring. Videotaped interviews with 23 psychiatric patients, most of whom had a clinical diagnosis of personality disorder, and a close informant were scored by seven raters, four in the United Kingdom and three in the United States. Overall inter-rater reliabilities (using the intraclass correlation coefficient, RI) were generally good to excellent for each of the 24 personality variables tested, ranging between .66 and .94 for informants and between .51 and .91 for subjects. Corresponding reliability coefficients for overall mean PAS scores were .82 and .75, respectively. Consistent with these findings, there was little bias between the scores of American and British raters, although there was some tendency for American raters to score higher for the trait of eccentricity and lower for the trait of conscientiousness than was true for British raters. There was less bias for informants' ratings than for those of subjects. In a second set of analyses, it was shown that inter-rater reliability levels (using the Kappa statistic) were also good to excellent (.6 to .8) for the categorical diagnosis of personality disorder. These results, taken together, demonstrate that abnormal personality can be reliably assessed by both British and American raters.

Adolescent↗
PubMed1983

Rotational freedom of tryptophan residues in proteins and peptides.

We studied the rotational motions of tryptophan residues in proteins and peptides by measurement of steady-state fluorescence anisotropies under conditions of oxygen quenching. By fluorescence quenching we can shorten the fluorescence lifetime and thereby decrease the average time for rotational diffusion prior to fluorescence emission. This method allowed measurement of rotational correlation times ranging from 0.03 to 50 ns, when the unquenched fuorescence lifetimes are near 4 ns. A wide range of proteins and peptides were investigated with molecular weights ranging from 200 to 80 000. Many of the chosen substances possessed a single tryptophan residue to minimize the uncertainties arising from a heterogeneous population of fluorophores. In addition, we also studied a number of multi-tryptophan proteins. Proteins were studied at various temperatures, under conditions of self-association, and in the presence of denaturants. A wide variety of rotational correlation times were found. As examples we note that the single tryptophan residue of myelin basic protein was highly mobile relative to overall protein rotation whereas tryptophan residues in human serum albumin, RNase T1, aldolase, and horse liver alcohol dehydrogenase were found to be immobile relative to the protein matrix. These results indicate that one cannot generalize about the extent of segmental mobility of the tryptophan residues in proteins. This physical property of proteins is highly variable between proteins and probably between different regions of the same protein.

Kinetics↗
PubMed1982

Theory of phase-modulation fluorescence spectroscopy for excited-state processes.

Theory is presented for the analysis of excited-state reactions by fluorescence phase shift and demodulation methods. Initially, a two-state model with spectral overlap is considered to illustrate most simply the effects of excited-state reactions on the expected phase and modulation values. Secondly, a multistate model is described to illustrate the probable effects of a fluorophore interacting with several solvent molecules. We note the following unique features of phase-modulation data expected from a fluorophore whose emission spectrum shifts during the lifetime of the excited state: (1) The modulation frequency dependence of the apparent phase (tau p) and modulation (tau m lifetimes of the reacted species is opposite to that of a heterogeneous population of fluorophores. (2) For the reacted species tau p greater than tau m. For a heterogeneous sample tau p less than tau m. (3) The phase angle of the reacted species can exceed 90 degrees. For a heterogeneous sample phase angles are always less than 90 degrees. Thus, phase and modulation measurements can distinguish between time-dependent processes and spectral heterogeneity by observation of any feature described above. Additionally: (4) The lifetime of the product species can be measured directly. (5) Reverse relaxation can be identified, and the reverse relaxation rates calculated. (6) The wavelength-dependent phase and modulation data can be used to resolve the individual spectra from a two-state reaction. (7) And finally, under favorable conditions, a two-state excited-state process can be distinguished from a continuous multiple-state process. In each instance, model calculations are presented to illustrate the unique potentials of phase-modulation fluorometry for investigations of excited-state processes.

Kinetics↗
PubMed1982

Analysis of excited-state processes by phase-modulation fluorescence spectroscopy.

Fluorescence phase shift and demodulation methods were used in the analysis of excited-state reactions and to investigate solvent relaxation around fluorophores in viscous solvents. The chosen samples illustrate the results expected for fluorophores bound to biological macromolecules. These moderately simple samples served to test the theoretical predictions described in the preceding paper (J.R. Lakowicz and A.B. Balter, Biophys. Chem. 16 (1982) 99.) and to illustrate the characteristic features of phase-modulation data expected from samples which display time-dependent spectral shifts. The excited-state protonation of acridine and exciplex formation between anthracene and diethylaniline provided examples of one-step reactions in which the lifetimes of the initially excited and the reacted species were independent of emission wavelength. Using these samples we demonstrated the following: (1) Wavelength-dependent phase shift and demodulation values can be used to prove the occurrence of an excited-state process. Proof is obtained by observation of phase angles (ø) larger than 90 degrees or by measurement of ratios of m/cos ø greater than 1, where m is the modulation of the emission relative to that of the excitation. (2) For a two-state process the individual emission spectra of each state can be calculated from the wavelength-dependent phase and modulation data. (3) The phase difference or demodulation factor between the initially excited and the reacted states reveals directly the fluorescence lifetime of the product of the reaction. (4) Phase-sensitive detection of fluorescence can be used to prove that the lifetimes of both the initially excited and the reacted states are independent of emission wavelength. (5) If steady-state spectra of the individual species are known, then phase-sensitive emission spectra can be used to measure the lifetimes of the individual components irrespective of the extent of spectral overlap. (6) Spectral regions of constant lifetime can be identified by the ratios of phase-sensitive emission spectra. In addition, we examined 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and N-acetyl-L-tryptophanamide (NATA) in viscous solvents where the solvent relaxation times were comparable to the fluorescence lifetimes. Using PRODAN in n-butanol we used m/cos ø measurements, relative to the blue edge of the emission, to demonstrate that solvent relaxation requires more than a single step. For NATA in propylene glycol we used phase-sensitive detection of fluorescence to directly record the emission spectra of the initially excited and the solvent relaxed states. These measurements can be easily extended to fluorophores which are bound to proteins and membranes and are likely to be useful in studies of the dynamic properties of biopolymers.

Biopolymers↗
PubMed1982

Differential-wavelength deconvolution of time-resolved fluorescence intensities. A new method for the analysis of excited-state processes.

We describe a new procedure for the analysis of time-resolved decays of fluorescence intensity observed for excited-state reactions. This procedure is particularly valuable because it simplifies both determination of the rate constants of excited-state reactions and calculation of the emission spectra of the unreacted and the reacted species. These advantages are obtained without additional data acquisition, by the further analysis of data which would already be collected. As is usual for an excited-state process, time-resolved decays of fluorescence intensity are collected at wavelengths across the emission spectrum. Generally, one derives analytical expressions for the impulse response by deconvolution using the time profile of the exciting pulse. We suggest that in addition to the procedure just described, the response observed at longer wavelengths be deconvolved using the response observed on the blue side of the emission. Typically, this emission is from the initially excited state of the fluorophore (F). Then, the derived decay time is the decay rate of the reacted species (R). In addition, spectral overlap of the F and R states is revealed quantitatively as an apparent zero-decay-time component in the derived impulse response function. This is because the population of the initially excited state is considered to be the excitation function. This spectral overlap component is easily quantified, and allows the emission spectra of the F and R states to be calculated. This deconvolution procedure requires one favorable circumstance, which is the ability to choose a wavelength at which only the initially excited state is emitting. We tested our procedure on the excited state protonation of acridine and the excited-state deprotonation of 2-naphthol. The former reaction is essentially irreversible, whereas depending upon pH the dissociation of 2-naphthol can be reversible. We demonstrated that this procedure, which we call differential-wavelength deconvolution, revealed the individual spectra and simplified determination of the kinetic constants from the time-resolved decays. Without differential-wavelength deconvolution considerably more complex methods are required. We expect this procedure to greatly facilitate the use of pulse fluorometry methods in the analysis of excited-state processes.

Acridines↗
PubMed1981

Correction of timing errors in photomultiplier tubes used in phase-modulation fluorometry.

The measurement of fluorescence lifetimes is known to be hindered by the wavelength-dependent and photocathode area-dependent time response of photomultiplier tubes. A simple and direct method is described to minimize these effects in photomultiplier tubes used for phase-modulation fluorometry. Reference fluorophores of known lifetime were used in place of the usual scattering reference. The emission wavelengths of the reference and sample were matched by either filters or a monochromator, and the use of a fluorophore rather than a scatterer decreases the differences in spatial distribution of light emanating from the reference and sample. Thus photomultiplier tube artifacts are minimized. Five reference fluorophores were selected on the basis of availability, ease of solution preparation, and constancy of lifetime with temperature and emission wavelength. These compounds are p-terphenyl, PPO, PPD, POPOP and dimethyl POPOP. These compounds are dissolved in ethanol to give standard solutions that can be used over the temperature range from -55 to +55 degrees C. Purging with inert gas is not necessary. The measured phase and modulation of the reference solution is used, in conjunction with the known reference lifetime, to calculate the actual phase and modulation of the excitation beam. The use of standard fluorophores does not require separate experiments to quantify photomultiplier effects, and does not increase the time required for the measurement of fluorescence lifetimes. Examples are presented which demonstrate the elimination of artifactual photomultiplier effects in measurements of the lifetimes of NADH (0.4 ns) and indole solutions quenched by iodide. In addition, the use of these reference solutions increases the accuracy of fluorescence lifetime measurements ranging to 30 ns. We judge this method to provide more reliable lifetime measurements by the phase and modulation method. The test solutions and procedures we describe may be used by other laboratories to evaluate the performance of their phase fluorometers.

Indicators and Reagents↗
PubMedDate not supplied

Infant circumcision.

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Circumcision, Male↗