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Biomedical subjects

L Packer

Publications and source records attributed to L Packer.

At least 361 records · Page 20Linked to original sources
PubMed1984

Exercise endurance-training alters vitamin E tissue levels and red-blood-cell hemolysis in rodents.

Muscle tissue levels of d1-alpha-tocopherol (vitamin E) were significantly lower in endurance-trained rats than in sedentary animals, whether the animals were fed on vitamin-E-deficient or control (vitamin-E-sufficient) diets. In vitamin-E-deficient rats, liver tissue levels of vitamin E were significantly lower in those that were endurance-trained than in those that were sedentary; this was not the case in control animals. In addition, for vitamin-E-deficient rats, the onset of red-blood-cell hemolysis in the sedentary animals occurred one week earlier than in the endurance-trained animals. Thus, it appears that training induces a protective effect against hemolysis despite vitamin E deficiency.

Animals↗
PubMed1984

Distinguishing effects of anemia and muscle iron deficiency on exercise bioenergetics in the rat.

Three weeks of dietary iron deficiency in weanling rats resulted in anemia (Hb, 3.9 vs. 14.2 g/dl in controls) and decreased oxidative capacities of skeletal muscle (as much as 90% below control values). Whole-animal maximal O2 consumption (VO2max), measured in a brief treadmill run of progressively increasing work load, was approximately 50% lower for iron-deficient rats than for controls, and maximal endurance capacity (time to exhaustion in a separate treadmill run at a constant, sub-Vo2max work load) was 90% lower for iron-deficient rats than for controls. Exchange transfusion, with packed erythrocytes or plasma, was used to adjust Hb to an intermediate concentration of approximately 9.5 g/dl in both iron-deficient and and control rats. This procedure corrected the Vo2max of iron-deficient rats to within 15% of control values, whereas endurance capacity showed no improvement. Our experimental dissociation of Vo2max and endurance capacity provides further evidence that Vo2max is not the sole determinant of endurance. We propose that defects in Vo2max during iron deficiency result primarily from diminished O2 delivery, whereas decreased endurance capacity reflects impaired muscle mitochondrial function.

Anemia, Hypochromic↗
PubMed1984

Spectroscopic characterization of nitrated purple membranes.

Light-adapted purple membranes were modified with tetranitromethane by a new light-dependent procedure at pH 5.5 which results in a blue-shifted chromophore absorbing at 530nm. This modification affects two aromatic residues. The modified bacteriorhodopsin's ground state chromophore structure is probed by circular dichroism and resonance raman spectroscopy while its photocycle is studied by laser-flash photolysis in the picosecond, microsecond and millisecond time scale. After nitration, the main findings are 1) Interactions between neighboring chromophores are lost, 2) Modified bacteriorhodopsin contains a conformationally changed chromophore but retains a protonated Schiff's base as evidenced by a resonance raman band at 1652 cm-1, 3) A red-shifted intermediate is formed in less than 10 ps after laser excitation, 4) The decay of the M-intermediate is not significantly affected whereas the rise time of the intermediate is enhanced about two fold. These observations are relevant to the role of aromatic acid residues of the apoprotein in the determination of the chromophoric characteristics in bacteriorhodopsin.

Bacteriorhodopsins↗
PubMed1983

Topographic studies of spin-labeled bacteriorhodopsin. Evidence for buried carboxyl residues and immobilization of the COOH-terminal tail.

Chemical modification and electron spin resonance techniques were used to study the topography of carboxyl residues in purple membranes. The results showed that buried carboxyl groups are located in hydrophobic protein domains at least 16 A from the membrane surface, and that the carboxyl-terminal tail is partially immobilized. Carboxyl groups on bacteriorhodopsin in purple membranes were covalently spin-labeled with 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl using N-(ethoxycarbonyl)-2-ethoxy-1,2-dihydroquinoline as a highly specific coupling agent. Spin-labeled bacteriorhodopsin preparations containing an average of 2.1 +/- 0.5 spins/molecule retained photocycling and proton-pumping functions. Accessibility to the paramagnetic broadening agents, Fe(CN)3-6 and Ni2+, revealed a highly mobile surface group quenched at low concentrations of these agents, and a buried, immobilized group whose ESR signal remained at high quencher concentration. Treatment with denaturing agents greatly increased the mobility and quenching of these buried residues. A series of stearic acid spin labels bound to purple membranes was used to define the depth of paramagnetic interactions. Fe(CN)3-6 interactions were limited to surfaces whereas Ni2+ and Cu2+ effects extended into hydrophobic domains. A double modification procedure, which first blocked surface groups, selectively spin-labeled only buried carboxyl group(s) having a strongly immobilized signal. ESR analysis of the isolated carboxyl-terminal tail after trypsin treatment showed it had increased mobility, indicating that it is moderately immobilized in the native structure. These data provide evidence consistent with several models of bacteriorhodopsin tertiary structure which place carboxyls within hydrophobic domains of the protein.

Amino Acid Sequence↗
PubMed1983

Evidence for a carboxyl group in the vicinity of the retinal chromophore of bacteriorhodopsin.

Carboxyl groups of bacteriorhodopsin in purple membranes were activated using a hydrophobic reagent and then covalently labeled with a pH-sensitive reporter group, nitrotyrosine methyl ester. The membrane-bound reporter group had different spectral properties, and a pK 3 units higher than in solution. In purple membranes, an isosbestic point between the 428nm absorption peak of nitrotyrosine methyl ester, and the bacteriorhodopsin 570nm chromophore seen in alkaline titration, indicated interactions between the reporter group and retinal. Modification of white membranes (bacterioopsin from R1mW strain) revealed similar, unusual spectral and ionization properties. Thus, the hydrophobic environment, not retinal interactions per se, are responsible for the ionization behavior of the reporter group. These results indicate that a carboxyl group is near the retinal chromophore of bacteriorhodopsin.

Bacteriorhodopsins↗
PubMed1983

Vitamin E, physical exercise and tissue oxidative damage.

Oxidative damage and the role of antioxidants and prooxidants in aerobic metabolism is of great current interest; it spans areas of research such as carcinogenesis, ageing, toxicology and nutrition. We have used Bantin-Kingman female rats for both in vivo and in vitro studies. In these animals we have altered the levels of all-rac-alpha-tocopherol (vitamin E) by dietary means and have used physical exercise and visible light exposure to alter oxidative stress. Our results show a progressive and specific increase in the susceptibility of many subcellular membranes to oxidative damage with increasing levels of vitamin E deficiency and/or physical stress. In addition, endurance training raised the levels of antioxidative enzymic pathways in both skeletal and cardiac muscle.

Animals↗
PubMed1983

Nonionic detergent effects on spectroscopic characteristics and the photocycle of bacteriorhodopsin in purple membranes.

Treatment of purple membranes isolated from Halobacterium halobium with nonionic detergents caused the following effects in addition to solubilizing bacteriorhodopsin: a blue shift of the absorption spectrum of bacteriorhodopsin; an increase in tryptophan fluorescence of about twofold; an enhanced rate of bleaching in the presence of hydroxylamine; and the disappearance of the negative exciton band in the CD spectrum at 600 nm. Crosslinking of purple membranes by glutaraldehyde can prevent solubilization of bacteriorhodopsin by detergents. However, only the effect on the CD spectrum by detergents can be inhibited by crosslinking of the purple membranes prior to detergent treatment. Photocycle kinetics studies revealed that the apparent pK of the slow component of the M412 decay was decreased by the detergent treatment while the rise time for M412 formation is accelerated two- to threefold. Crosslinking also did not prevent these effects. These results demonstrate that nonionic detergents, apart from their action to monomerize bacteriorhodopsin, also affect retinal-apoprotein interactions.

Bacteriorhodopsins↗
PubMed1983

Light-dependent nitration of bacteriorhodopsin.

Purple membranes were treated with tetranitromethane to modify tyrosine residues of bacteriorhodopsin. At pH 8.0, nitration is shown to be affected by illumination during the modification. Amino acid analysis revealed about 0.7 residues nitrated if reaction was in the dark while about 2.0 tyrosines were modified if illumination greater than 540 nm was provided. Tryptophan was unaffected under both conditions. Light-dependent nitration caused a blue shift of the absorbance maximum of bacteriorhodopsin from 568 to 530 nm while no chromophore shift was observed for the dark-modified preparation. Both preparations show an absorption band at 360 nm indicative of the presence of nitrotyrosines. Reduction by dithionite eliminated the pH-dependent changes associated with the 360-nm nitrotyrosine band. Circular dichroism spectra indicate that interactions between neighboring chromophores are altered concomitant with the blue shift of the absorbance maximum by nitration. These studies show that light is required for the nitration of the tyrosine residue, and that Tyr 26 (H. D. Lemke and D. Oesterhelt (1981) Eur. J. Biochem. 115, 595-604) is probably responsible for the blue shift of the absorbance maximum. The intrinsic fluorescence and photocycle kinetics of the tyrosine-modified preparation and reduction of nitrotyrosine by dithionite were studied. In dark modification, only pH-dependent dithionite-reducible nitrotyrosines were produced. It is concluded that surface tyrosines probably do not directly participate in the proton-translocation events coupled to the photocycle of bacteriorhodopsin.

Bacteriorhodopsins↗
PubMed1983

Studies of osmoregulation in salt adaptation of cyanobacteria with ESR spin-probe techniques.

Sucrose is accumulated in response to NaCl-induced stress in the cyanobacterium Synechococcus 6311. Internal cell volume was measured by ESR spectra with 2,2,6,6-tetramethyl-4-oxopiperidinoxy free radical (TEMPONE) as a spin probe in order to calculate sucrose concentrations inside the cell. This method is rapid and reliable and provides an unambiguous measurement of absolute volumes in different osmotic environments. Because the osmolar concentration of sucrose does not counter-balance the osmolar concentrations of ions in the growth medium, we suggest that sucrose accumulation is one of the mechanisms involved in the process of adaptation to salt of Synechococcus 6311. The accumulation of sucrose in non-N(2)-fixing cyanobacteria such as Synechococcus 6311 and in N(2)-fixing cyanobacteria such as Nostoc muscorum suggests a common mechanism of osmoregulation of fresh water cyanobacteria in response to increasing NaCl concentrations in the growth medium.

Journal Article↗
PubMed1983

Ionic Osmoregulation during Salt Adaptation of the Cyanobacterium Synechococcus 6311.

The mechanisms of salt adaptation were studied in the cyanobacterium Synechococcus 6311. Intracellular volumes and ion concentrations were measured before and after abrupt increases of external NaCl concentrations up to 0.6 molar NaCl. Equilibrium volumes, measured with a rapid and accurate electron spin resonance spin probe method, showed that at low NaCl concentrations the cells did not shrink as expected for an impermeable solute. However, when the NaCl concentration exceeded a critical value, volume losses occurred. These losses were not fully reversed by hypoosmotic treatment, suggesting membrane damage. The critical value of irreversible volume loss paralleled the increase in salinity during cell growth. Rapid mixing experiments showed that exposure of Synechococcus 6311 to non-damaging NaCl concentrations caused water extrusion from the cells; the volume decreases were time resolved to about 200 milliseconds. Subsequently, volumes increased rapidly as NaCl moved into the cells. Controls recovered their volumes within 15 seconds, while salt-adapted cells grown at 0.6 molar NaCl required 1 minute for volume equilibration. This decrease in the rate of cell volume recovery indicates that salt adaptation is accompanied by changes in cell membrane properties. Subsequent to these initial rapid volume changes, a more gradual sequence of ion movement and sugar accumulation was observed. Under conditions for photoautotrophic growth, significant Na(+) extrusion was observed 30 min after salt shock. Sucrose accumulation reached a maximum value after 16 hours and K(+) accumulation reached equilibrium after 40 hours. The final concentrations of K(+) and Na(+) and sucrose and glucose inside the 0.6 molar NaCl-grown cells indicate that the inorganic ions and organic ;compatible' solutes are the major osmotic species which account for the adaptation of Synechococcus 6311 to salt.

Journal Article↗