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A Defective Proton Pump, Point-Mutated Bacteriorhodopsin Asp96 → Asn Is Fully Reactivated by Azide

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Tittor,  Jörg
Oesterhelt, Dieter / Membrane Biochemistry, Max Planck Institute of Biochemistry, Max Planck Society;

Soell,  Christa
Oesterhelt, Dieter / Membrane Biochemistry, Max Planck Institute of Biochemistry, Max Planck Society;

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Oesterhelt,  Dieter
Oesterhelt, Dieter / Membrane Biochemistry, Max Planck Institute of Biochemistry, Max Planck Society;

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Butt,  Hans J.
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Bamberg,  Ernst
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Tittor, J., Soell, C., Oesterhelt, D., Butt, H. J., & Bamberg, E. (1989). A Defective Proton Pump, Point-Mutated Bacteriorhodopsin Asp96 → Asn Is Fully Reactivated by Azide. The EMBO Journal, 8(11), 3477-3482. doi:10.1002/j.1460-2075.1989.tb08512.x.


Cite as: http://hdl.handle.net/21.11116/0000-0006-97F7-9
Abstract
Addition of azide fully restored the proton pump activity of defective bacteriorhodopsin (BR) mutant protein Asp96 → Asn. The decay time of M of BR Asp96 → Asn, the longest living intermediate, was decreased from 500 ms at pH 7.0 to approximately 1 ms under conditions of saturating azide concentrations. This decay was faster than the decay of M in the wild-type, where no such azide effect was detectable. Stationary photocurrents, measured with purple membranes immobilized and oriented in a polyacrylamide gel, increased upon addition of azide up to the level of the wild-type. Different small anions of weak acids restored the pump activity with decreasing affinity in the order: cyanate greater than azide greater than nitrite greater than formiate greater than acetate. The activation energy of the M decay in the mutant was higher in the presence (48 kJ/mol) than in the absence (27 kJ/mol) of 100 mM azide even though the absolute rate was dramatically increased by azide. This effect of azide is due to the substitution of a carboxamido group for a carboxylic group at position 96 which removes the internal proton donor and causes an increase in the entropy change of activation for proton transfer which is reversed by azide.