On the mechanism of sodium ion translocation by oxaloacetate decarboxylase of Klebsiella pneumoniae.
Proteoliposomes reconstituted with purified oxaloacetate decarboxylase of Klebsiella pneumoniae catalyzed the uptake of Na+ ions upon oxaloacetate decarboxylation. The degree of coupling between the chemical and the vectorial reaction is dependent on the reconstitution conditions, and with the best preparations approaches a stoichiometry of two Na+ ions per decarboxylation of one oxaloacetate. This coupling ratio is observed only in the absence of a delta mu Na+, immediately after oxaloacetate addition. The ratio gradually declines during development of the electrochemical Na+ ion gradient and becomes zero in the steady state. The Na+ pump, however, continued to decarboxylate oxaloacetate and to catalyze Na+ influx at the apparent stoichiometry of two Na+ ions per decarboxylation event. During the steady state, this influx must be compensated by Na+ efflux of the same size. The efflux is catalyzed by the Na+ pump upon oxaloacetate decarboxylation, because in the absence of the substrate the efflux rate dropped to less than 10%. Proteoliposomes loaded with Na2SO4 catalyzed a bicarbonate-dependent uptake of 22Na+ that was completely abolished after incubation with avidin. These results suggest coupling of Na+ translocation to the carboxylation/decarboxylation of the biotin prosthetic group without the requirement for the oxaloacetate/pyruvate interconversion. The oxaloacetate-dependent transport of Na+ into proteoliposomes was inhibited by the additional presence of the beta + gamma subunits of oxaloacetate decarboxylase. A model of Na+ translocation by oxaloacetate decarboxylase based on these experimental results is proposed.
Dimroth
P
P
Mikrobiologisches Institut, Eidgenössischen Technischen Hochschule, Zürich, Switzerland.
Thomer
A
A
D001360:Avidin / Q000494:pharmacology; D001639:Bicarbonates / Q000494:pharmacology; D001692:Biological Transport; D002262:Carboxy-Lyases / Q000378:metabolism*; D002414:Cations, Monovalent; D004563:Electrochemistry; D007700:Kinetics; D007711:Klebsiella pneumoniae / Q000201:enzymology*; D008081:Liposomes / Q000378:metabolism; D017830:Octoxynol; D010071:Oxaloacetates / Q000378:metabolism; D011092:Polyethylene Glycols / Q000494:pharmacology; D017680:Potassium Compounds; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology; D014634:Valinomycin / Q000494:pharmacology
D001639:Bicarbonates; D002414:Cations, Monovalent; D008081:Liposomes; D010071:Oxaloacetates; D017680:Potassium Compounds; D001360:Avidin; D014634:Valinomycin; D011092:Polyethylene Glycols; D017830:Octoxynol; D012964:Sodium; D002262:Carboxy-Lyases; C021916:oxaloacetate decarboxylase; D000254:Sodium-Potassium-Exchanging ATPase; C026329:potassium bicarbonate