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Biomedical subjects

M Skonieczna

Publications and source records attributed to M Skonieczna.

At least 19 recordsLinked to original sources
PubMed1999

The photochemical attachment of the O-glucoside of 3-hydroxykynurenine to alpha-crystallin: a model for lenticular aging.

The young human lens contains a small metabolite from tryptophan called the O-glucoside of 3-hydroxykynurenine (3-HKG). Its function is to absorb most radiation between 295 and 400 nm, preventing it from reaching the retina. With age the concentration of this component decreases while the lens crystallins acquire covalently attached chromophores. This study investigates the photochemical attachment of 3-HKG to lens alpha-crystallin. Initial studies showed that alpha-crystallin photolyzed in the presence of 3-HKG developed a fluorescence (emission, 440 nm) and UV-visible spectrum similar to that found in aged human lens proteins. Extensive studies were then performed on the tryptic HPLC maps as monitored by photodiode array and fluorescent detection. Numerous photoproducts with either blue (emission, > 400 nm) or green (emission, > 500 nm) fluorescence were formed in addition to nonfluorescent compounds with absorption maxima above 300 nm. Comparisons were made between these model photoproducts and peptide maps from alpha-crystallin isolated from old human lenses. In terms of retention time and UV-visible spectra at least two of the peptides that appear in the model system are also present in the human samples. It is concluded that one of the aging processes in the human lens is the photochemically induced attachment of 3-HKG to lens proteins.

Aging↗
PubMed1986

Influence of repeated exposure to elevated environmental temperature on the activity of respiratory enzymes of rat liver mitochondria.

The paper presents studies of the activity of lipid-dependent enzymes of the respiratory chain of the liver of rats exposed to increased ambient temperature. The animals were heated in a chamber under controlled humidity (45-55% relative humidity), with forcer air flow and regulated temperature of 21 degrees +/- 1 degree C (control group) and 28 degrees +/- 1 degree C or 35 degrees +/- 1 degree C. They were affected by a relevant temperature for 7 or 14 consecutive days, 6 hrs daily. The enzymes activities were determined in a fraction of submitochondrial particles. The studies demonstrated that under the increased ambient temperature (7 X 6 hrs), the activity of the respiratory enzymes is changed. A statistically significant increase in the activity of NADH dehydrogenase, NADH cytochrome c reductase and cytochrome oxidase was found along with a decrease in the activity of succinate cytochrome c reductase and succinate dehydrogenase. On prolongation of thermal exposure (14 X 6 hrs) the activity of succinate dehydrogenase and succinate reductase: cytochrome c was further decreased. The activities of the other test enzymes did not exhibit any statistically significant differences as compared to controls. Kinetic tests of succinate dehydrogenase point to conformational changes of the enzyme when affected by an increased ambient temperature. This confirms the important role of this enzyme in the animals adaptation to thermally varying environmental conditions.

Animals↗
PubMed1984

Respiratory activity and oxidative phosphorylation in mitochondria of the rat brain and liver under conditions of elevated temperature of the environment.

The rate of oxygen consumption by mitochondrial fractions of the brain and liver of rats under elevated ambient temperature was investigated. The animals were placed in a thermostatized chamber for 6 hours at 21 degrees, 28 degrees or 37 degrees C. During the experiment, relative humidity in the chamber was controlled. After exposure, the animals were decapitated, mitochondrial fractions isolated and oxygen consumption measured with the Clark electrode. Respiratory substrates of succinate and glutaminate with malate were used. The analysis of the obtained results was based on the t-Student test, assuming the values obtained for the animals staying at 21 degrees as the control values. It was found that the 6 hrs stay under the ambient hyperthermy conditions did not induce any disturbances in the respiratory processes and oxidative phosphorylation in rat's brain and liver mitochondria.

Animals↗
PubMed1982

Modification of brain mitochondrial enzymes by the oxygen analogue of ronnel at various stages of development and aging.

This paper describes the effect of the organophosphorus compound, the oxygen analogue of ronnel (OAR), on the activity of some membrane-bound enzyme systems in the brain mitochondria of developing, young-adult, and old rats. Age-related changes were noted in the cholesterol-to-protein ratio, whereas the phospholipid content in mitochondria showed little change during development as well as aging. The results obtained suggest that development of brain succinate dehydrogenase may consist in a decrease of Km and increase of Vmax values. In aged rats an altered, perhaps inhibited form of the enzyme is produced. The oxygen analogue of ronnel caused a mixed-type inhibition of the succinate dehydrogenase derived from brains of 4-day-old, 16-day-old and 2-month-old animals. In the case of enzyme from the brain of 18-month-old rats, a typical competitive-type inhibition was observed. Mechanisms responsible for inhibition of the succinate: cytochrome c reductase from brains of developing animals are similar to those for succinate dehydrogenase. In aged rats (18 months old), however, a noncompetitive mechanism of inhibition of succinate: cytochrome c reductase was revealed. The experiments reported here provide evidence that lipid-soluble molecules of OAR may interact with membrane phospholipids and lead to modification of membrane architecture and also of enzyme kinetic behaviour. It may be also concluded, that the sensitivity of the enzyme systems studied to inhibition by OAR is an age-dependent phenomenon. Modification of membrane by development or aging alters the kinetics as well as the sensitivity of enzymes to inhibitors.

Aging↗
PubMed1980

Ultrastructural and biochemical studies of the brain and other organs in rat after chronic ethanol administration. III. Influence of ethanol intoxication on oxidative phosphorylation of the rat brain mitochondria with ultrastructural and morphometric evaluation of mitochondrial fraction).

The effect of chronic ethanol intoxication on oxidative phosphorylation in the rat brain mitochondrial fraction was examined. Moreover, electron microscopy was used to verify the quantitative composition of the fraction and for examination of ultrastructural changes in the mitochondria. The experiments were carried out with 60 rats receiving, beside the normal diet, ethyl alcohol according to a modified RATCLIFFE model. In isolated rat brain mitochondria the NAD-dependent oxidation of substrates (glutamate + malate) was decreased. The phosphorylation index ADP/0 and the respiratory control ratio (RCR) in rat brain mitochondria from ethanol-treated rats were unchanged in the presence of both succinate and glutamate + malate. Chronic ethanol feeding did not induce any changes of succinate dehydrogenase and cytochrome oxidase activities in solubilised mitochondria fractions of rat brain. Electron microscopy studies revealed that mitochondria from control animals retained their outer and inner membranes, whereas those from rats given ethanol were almost always swollen and some were disrupted. In mitochondrial fractions isolated from ethanol-intoxicated rats an increase was observed of contaminating elements i.e. axons and synaptosomes of various sizes. It should be stressed that the mitochondria located inside synaptosomes and axons were unchanged. The composition of the fractions was quantitatively evaluated and confirmed the diminution of "free" mitochondria in the experimental fractions in favour of "bound" mitochondria which mainly occurred in the synaptosomes with preserved metabolic activity. On the basis of electron microscopy studies it could be suggested that ethanol intoxication causes the damage of some mitochondria, which become more sensitive to mechanical destruction during isolation procedure, and they do not sediment together with the fraction of normal ones. The absence of "free" mitochondria in pellets explains the spurious lack of disturbances in the energy metabolism of brain mitochondria after chronic ethanol intoxication.

Adenosine Diphosphate↗