ISSN:
1432-072X
Keywords:
Key wordsPenicillium simplicissimum
;
Efflux of
;
citrate
;
Efflux of isocitrate
;
Basal permeability
;
Specific excretion system
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Penicillium simplicissimum excreted citrate, isocitrate, and succinate when grown in a strongly buffered medium [1 M Mes (pH 6) or 1 M Hepes (pH 7.3)]. Growth in a weakly buffered medium did not lead to citrate excretion despite a similar intracellular citrate concentration. When nongrowing, citrate-excreting hyphae were aerated in a glucose solution, the following steady-state intracellular concentrations of organic acids were measured: succinate (25 mM); citrate, isocitrate, malate, and fumarate (all less than 5 mM). After 2 h of incubation, the extracellular concentrations of these acids were [μmol (g dry wt.)–1]: isocitrate [100], citrate [60], succinate [30], and malate, fumarate, and α-ketoglutarate [〈5]. The excretion of citrate was due neither to an unspecific change in the permeability of the plasma membrane nor to simple diffusion of undissociated citric acid. The involvement of a transport protein in citrate excretion was indicated because N-ethylmaleimide and sodium azide inhibited citrate excretion strongly despite an unchanged outward-directed citrate gradient. Arguments are given why efflux via a citrate uptake carrier is not considered probable. These results indicate that citrate is excreted by P. simplicissimum via a transport protein that probably specifically mediates the efflux of citrate.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002030050582
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