1887

Abstract

Trophozoites of the microaerophilic flagellate parasitic protozoon have only a limited capacity to detoxify O. Thus, when exposed to controlled concentrations of dissolved O >8 μM, they gradually lose their ability to scavenge O. In a washed cell suspension stirred under 10% air in N (equivalent to 25 μM O), inactivation of the O-consuming system was complete after 35 h; during this period accumulation of HO (3 μmol per 10 organisms) and oxidation of cellular thiols to 16% of their initial level occurred. Under 20% air (50 μM O), respiratory inactivation was complete after 15 h, and under air (258 μM O), after 50 min. Loss of O-consuming capacity was accompanied by loss of motility. Use of the fluorogen 2,7-dichlorodihydrofluorescein acetate indicated that intracellular HO is produced at extranuclear sites. Flow cytometric estimation of the plasma membrane electrochemical potentials using bis(1,3-dibutylbarbituric acid) trimethine oxonol, DiBAC(3), showed that values declined from −134 mV to −20 mV after 45 h aeration. Incubation of organisms with 60 μM HO for 10 min gave partial collapse of plasma membrane potential and complete loss of O uptake capacity; motility and viability as assessed by DiBAC(3) exclusion were completely lost after 1 h. Inactivation of the O-consuming system and loss of viability were also observed on exposure to singlet oxygen photochemically generated from rose bengal or toluidine blue.

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2000-12-01
2020-03-29
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