Characterization of an inducible citrate uptake system in Penicillium simplicissimum.
When citrate was used as a sole source of carbon, citrate uptake by Penicillium simplicissimum increased 267-fold (if glucose-grown mycelium was adapted to citrate) or 1400-fold (if the fungus was grown on citrate) compared to glucose-grown mycelium. Inhibition of macromolecular synthesis prevented this stimulation of citrate uptake. Citrate uptake by glucose-grown mycelium was low (0.0015 nmol min(-1) (mg DW)(-1)) and most probably due to diffusion of undissociated citric acid. Citrate-adapted mycelium had a K(M) of 65 micromol l(-1) and a V(max) of 0.34 nmol min(-1) (mg DW)(-1). In citrate-grown mycelium K(M) was 318 micromol l(-1) and V(max) was 8.5 nmol min(-1) (mg DW)(-1). Citrate uptake was inhibited by sodium azide and uncouplers (TCS, 3,3',4',5-tetrachlorosalicylanilide; FCCP, carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone). Because of this we postulate that the induced citrate uptake must be an active transport process. The pH optimum of citrate uptake was between pH 6 and 7. EDTA and Mg2+, Mn2+, Cu2+, Zn2+, Fe2+, Ca2+ only weakly influenced the induced citrate uptake. The properties of citrate uptake by Aspergillus niger and P. simplicissimum are compared.
Department of Biochemistry and Microbiology, Slovak University of Technology, Radlinského 9, Bratislava, Slovak Republic.
Martin
M
Simkovic
Michal
M
Kalinák
Wolfgang
W
Burgstaller
L'udovít
L
Varecka
D001692:Biological Transport; D019343:Citric Acid / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010407:Penicillium / Q000254:growth & development / Q000378:metabolism*; D019810:Sodium Azide / Q000037:antagonists & inhibitors
D019343:Citric Acid; D019810:Sodium Azide