The light-induced absorbance change around
5 15 nm (aAs15) in chloroplasts has been attributed
mainly to the electrochromic response of pigments
embedded in the thylakoid membranes [ 11. This
change in absorbance, related to the energized state
of the thylakoids, starts with a fast (-IX) rise and
relaxes with a slow (-100 ms) decay [2,3]. Recently,
in intact isolated chloroplasts a biphasic rise, has been
established [4-91. The slow phase of the rise in
aAsl5 has been explained in various ways. The most
common view is that the slow rise of A.4 515is connected with the reduction of cytochrome fand to an
inward translocation of protons [5,8,10].
This paper provides additional, direct evidence to
support this idea by analysing the kinetics of the
flash-induced Msls in a medium where ‘Hz0 was
replaced by ‘H1O. Furthermore, from an analysis of
the temperature dependence of the kinetic components of A,4515, we conclude that slow rise and decay
represent different proton translocation processes as
shown by their different activation energies.
The light-induced absorbance change around5 15 nm (aAs15) in chloroplasts has been attributedmainly to the electrochromic response of pigmentsembedded in the thylakoid membranes [ 11. Thischange in absorbance, related to the energized stateof the thylakoids, starts with a fast (-IX) rise andrelaxes with a slow (-100 ms) decay [2,3]. Recently,in intact isolated chloroplasts a biphasic rise, has beenestablished [4-91. The slow phase of the rise inaAsl5 has been explained in various ways. The mostcommon view is that the slow rise of A.4 515is connected with the reduction of cytochrome fand to aninward translocation of protons [5,8,10].This paper provides additional, direct evidence tosupport this idea by analysing the kinetics of theflash-induced Msls in a medium where ‘Hz0 wasreplaced by ‘H1O. Furthermore, from an analysis ofthe temperature dependence of the kinetic components of A,4515, we conclude that slow rise and decayrepresent different proton translocation processes asshown by their different activation energies.
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