Beitrag zur Flora von Bosnien und der Hercegovina

Ohne Zusammenfassung     

MährischeThymus-Formen

Ohne Zusammenfassung     

Beitrag zur Flora der Beskiden und des Hochgesenkes

Ohne Zusammenfassung     

Regulation of acid hydrolysis of sucrose in acid lime juice sac cells

The sucrose content of acid lime [ Citrus aurantifolia (Christm.) Swing.] juice tissue was measured at time 0 and at various times following incubation at 15.5, 26.6 and 37.7°C. The decline in sucrose content in fruit stored at 15.5°C paralleled the expected values for a sucrose solution at pH 2.1. At higher temperatures, the in vivo sucrose content decreased at significantly lower rates than the expected values. In fruit stored at 26.6 and 37.7°C, the vacuolar pH increased 0.11 and 0.23 units, respectively. When sucrose hydrolysis was recalculated at the increased vacuolar pH of juice cells stored at 26.6 and 37.7°C, the calculated values were similar to the measured values obtained in vivo. It is concluded that within the limits of the experimental conditions, the rates of sucrose acid hydrolysis are regulated by changes in the vacuolar H⁺ concentration.     

The specificity of thiourea, dimethylthiourea and dimethyl sulphoxide as scavengers of hydroxyl radicals. Their protection of alpha 1-antiproteinase against inactivation by hypochlorous acid.

Thiourea and dimethylthiourea are powerful scavengers of hydroxyl radicals (.OH), and dimethylthiourea has been used to test the involvement of .OH in several animal models of human disease. It is shown that both thiourea and dimethylthiourea are scavengers of HOCl, a powerful oxidant produced by neutrophil myeloperoxidase. Hence the ability of dimethylthiourea to protect against neutrophil-mediated tissue damage cannot be used as evidence for a role of .OH in causing such damage. Dimethyl sulphoxide also reacts with HOCl, but at a rate that is probably too low to be biologically significant at dimethyl sulphoxide concentrations up to 10 mM. Neither mannitol nor desferrioxamine, at the concentrations normally used in radical-generating systems, appears to react with HOCl.     

Cobalt(II) ion as a promoter of hydroxyl radical and possible 'crypto-hydroxyl' radical formation under physiological conditions. Differential effects of hydroxyl radical scavengers

Co(II) ions react with hydrogen peroxide under physiological conditions to form a 'reactive species' that can hydroxylate aromatic compounds (phenol and salicylate) and degrade deoxyribose to thiobarbituric-acid-reactive material. Catalase decreases the formation of this species but superoxide dismutase or low concentrations of ascorbic acid have little effect. EDTA, present in excess over the Co(II), can accelerate deoxyribose degradation and aromatic hydroxylation. In the presence of EDTA, deoxyribose degradation by the reactive species is inhibited competitively by scavengers of the hydroxyl radical (.OH), their effectiveness being related to their second-order rate constants for reaction with .OH. In the absence of EDTA the scavengers inhibit only at much higher concentrations and their order of effectiveness is changed. It is suggested that, in the presence of EDTA, hydroxyl radical is formed 'in free solution' and attacks deoxyribose or an aromatic molecule. In the absence of EDTA, .OH radical is formed in a 'site-specific' manner and is difficult to intercept by .OH scavengers. The relationship of these results to the proposed 'crypto .OH' radical is discussed.     

Cobalt(II) ion as a promoter of hydroxyl radical and possible ‘crypto-hydroxyl’ radical formation under physiological conditions. Differential effects of hydroxyl radical scavengers

Co(II) ions react with hydrogen peroxide under physiological conditions to form a ‘reactive species’ that can hydroxylate aromatic compounds (phenol and salicylate) and degrade deoxyribose to thiobarbituric-acid-reactive material. Catalase decreases the formation of this species but superoxide dismutase or low concentrations of ascorbic acid have little effect. EDTA, present in excess over the Co(II), can accelerate deoxyribose degradation and aromatic hydroxylation. In the presence of EDTA, deoxyribose degradation by the reactive species is inhibited competitively by scavengers of the hydroxyl radical (OH), their effectiveness being related to their second-order rate constants for reaction with OH. In the absence of EDTA the scavengers inhibit only at much higher concentrations and their order of effectiveness is changed. It is suggested that, in the presence of EDTA, hydroxyl radical is formed ‘in free solution’ and attacks deoxyribose or an aromatic molecule. In the absence of EDTA, OH radical is formed in a ‘site-specific’ manner and is difficult to intercept by OH scavengers. The relationship of these results to the proposed ‘crypto OH’ radical is discussed.     

Formation of hydroxyl radicals in the presence of ferritin and haemosiderin. Is haemosiderin formation a biological protective mechanism?

Horse spleen and human spleen ferritins increase the formation of hydroxyl radicals (OH) at both pH 4.5 and pH 7.4 in reaction mixtures containing ascorbic acid and H2O2. The generation of OH is inhibited by the chelator desferrioxamine. Human spleen haemosiderin also accelerates OH generation in identical reaction mixtures, but is far less effective (on a unit iron basis) than ferritin under all reaction conditions. It is proposed that conversion of ferritin into haemosiderin in iron overload is biologically advantageous in that it decreases the ability of iron to promote oxygen-radical reactions.