ISSN:
1432-1424
Schlagwort(e):
flash spectrophotometry
;
unit conductance
;
gramicidin
;
proton conduction
;
CF0
;
ATP synthase
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Chemie und Pharmazie
Notizen:
Summary We previously introduced a flash spectrophotometric method to analyze proton conduction by CF0 in vesicles derived from thylakoid membranes (H. Lill, S. Engelbrecht, G. Schönknecht & W. Junge, 1986,Eur. J. Biochem. 160:627–634). The unit conductance of CF0, as revealed by this technique, was orders of magnitude higher than that theoretically expected for a hydrogen-bonded chain. We scrutinized the validity of this method. Small vesicles were derived from thylakoids by EDTA treatment. The intrinsic electric generators in the membrane were stimulated by short flashes of light and the relaxation of the voltage via ionic channels was measured through electrochromic absorption changes of intrinsic pigments. The voltage decay was stimulated by a statistical model. As the vesicle-size distribution had only a minor influence, the simulation required only two fit parameters, the first proportional to the unit conductance of an active channelG, and the second denoting the average number of active channels per vesiclen. This technique was applied to CF0, the proton channel of the chloroplast ATP synthase, and to gramicidin, serving as a standard. For both channels we found the above two fit parameters physically meaningful. They could be independently varied in predictable wasy, i.e.n by addition of known inhibitors of F0-type proton channels andG via the temperature. for gramicidin, the unit conductance (2.7 pS) was within the range described in the literature. This established the competence of this method for studies on the mechanism of proton conduction by CF0, whose conductance so far has not been accessible to other, more conventional approaches. The time-averaged unit conductance of CF0 was about 1 pS, equivalent to the turnover of 6×105 H+/(CF0·sec) at 100 mV driving force.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF01871046
Permalink
