TAILIEUCHUNG - Báo cáo Y học: Intracellular pH homeostasis in the filamentous fungus Aspergillus niger

Intracellular pH homeostasis in the filamentous fungus Aspergillus niger was measured in real time by 31P NMR during perfusion in the NMR tube of fungal biomass immobilized in Ca2+-alginate beads. The fungus maintained constant cytoplasmic pH (pHcyt) and vacuolar pH (pHvac) values of and , respectively, when the extracellular pH (pHex) was varied between and in the presence of citrate. Intracellular metabolism did not collapse until a DpH over the cytoplasmic membrane of – was reached (pHex –). Maintenance of these large pH differences was possible without increased respiration compared to pHex | Eur. J. Biochem. 269 3485-3494 2002 FEBS 2002 doi Intracellular pH homeostasis in the filamentous fungus Aspergillus niger Stephan J. A. Hesse1 George J. G. Ruijter2 Cor Dijkema1 and Jaap Visser2 t 1 Department of Biophysics Wageningen University the Netherlands department of Microbiology section Fungal Genomics Wageningen University the Netherlands Intracellular pH homeostasis in the filamentous fungus Aspergillus niger was measured in real time by 31P NMR during perfusion in the NMR tube of fungal biomass immobilized in Ca2 -alginate beads. The fungus maintained constant cytoplasmic pH pHcyt and vacuolar pH pHvac values of and respectively when the extracellular pH pHex was varied between and in the presence of citrate. Intracellular metabolism did not collapse until a ApH over the cytoplasmic membrane of was reached pHex . Maintenance of these large pH differences was possible without increased respiration compared to pHex . Perfusion in the presence of various hexoses and pentoses pHex revealed that the magnitude of ApH values over the cytoplasmic and vacuolar membrane could be linked to the carbon catabolite repressing properties of the carbon source. Also larger ApH values coincided with a higher degree of respiration and increased accumulation of polyphosphate. Addition of protonophore carbonyl cyanide m-chlorophenylhydrazone CCCP to the perfusion buffer led to decreased ATP levels increased respiration and a partial 1 M CCCP transient 2 M CCCP or permanent 10 M CCCP collapse of the vacuolar membrane ApH. Nonlethal levels of the metabolic inhibitor azide N3- mM caused a transient decrease in pHcyt that was closely paralleled by a transient vacuolar acidification. Vacuolar H influx in response to cytoplasmic acidification also observed during extreme medium acidification indicates a role in pH homeostasis for this organelle. Finally 31P NMR spectra of citric acid producing A. niger .

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