The Kok Cycle
Phuruthrmisrrv und Photobiolugy.
1970. Vol. 1 I , pp. 457-475.
Pcrgamon Press.
Printed in Great Britain
COOPERATION OF CHARGES IN PHOTOSYNTHETIC 0,
EVOLUTION - I.
A LINEAR FOUR STEP MECHANISM
BESSEL KOK, BLISS FORBUSH and MARION McGLOlN
Research Institute for Advanced Studies, 1450 South Rolling Road, Baltimore, Md. 2 1227, U.S.A.
(Received I9 September 1969;in revised form 29 December 1969)
Abstract- Using isolated chloroplasts and techniques as described by Joliot and Joliot [6] we studied the evolution of 0, in weak light and light flashes to analyze the interactions between light induced 0, precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents
2.
either as precursor or as 02. The number of unstable precursor equivalents present during steady state photosynthesis is = 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final 0, evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, (S) successively accumulates four charges. The S4+state produces O2and returns to the ground state S,,. 5. Besides So also the first oxidized state S+ is stable in the dark, the two higher states,
Sp+ and S3+are not. 6. The relaxation times of some of the photooxidation steps were estimated.
:
:
The fastest reaction, presumably S + S,, has a (first) half time < 200 psec. The S state and probably also the SJ state are processed somewhat more slowly (- 300-400psec).
+
INTRODUCTION
ALLENand Franck [ 13 noticed that in darkness the photosynthetic apparatus looses its ability to produce 0, in a single flash, an observation which was confirmed e.g. by Whittingham and Bishop[2]. More recently, with the aid of
1970. Vol. 1 I , pp. 457-475.
Pcrgamon Press.
Printed in Great Britain
COOPERATION OF CHARGES IN PHOTOSYNTHETIC 0,
EVOLUTION - I.
A LINEAR FOUR STEP MECHANISM
BESSEL KOK, BLISS FORBUSH and MARION McGLOlN
Research Institute for Advanced Studies, 1450 South Rolling Road, Baltimore, Md. 2 1227, U.S.A.
(Received I9 September 1969;in revised form 29 December 1969)
Abstract- Using isolated chloroplasts and techniques as described by Joliot and Joliot [6] we studied the evolution of 0, in weak light and light flashes to analyze the interactions between light induced 0, precursors and their decay in darkness. The following observations and conclusions are reported: 1. Light flashes always produce the same number of oxidizing equivalents
2.
either as precursor or as 02. The number of unstable precursor equivalents present during steady state photosynthesis is = 1.2 per photochemical trapping center. 3. The cooperation of the four photochemically formed oxidizing equivalents occurs essentially in the individual reaction centers and the final 0, evolution step is a one quantum process. 4. The data are compatible with a linear four step mechanism in which a trapping center, or an associated catalyst, (S) successively accumulates four charges. The S4+state produces O2and returns to the ground state S,,. 5. Besides So also the first oxidized state S+ is stable in the dark, the two higher states,
Sp+ and S3+are not. 6. The relaxation times of some of the photooxidation steps were estimated.
:
:
The fastest reaction, presumably S + S,, has a (first) half time < 200 psec. The S state and probably also the SJ state are processed somewhat more slowly (- 300-400psec).
+
INTRODUCTION
ALLENand Franck [ 13 noticed that in darkness the photosynthetic apparatus looses its ability to produce 0, in a single flash, an observation which was confirmed e.g. by Whittingham and Bishop[2]. More recently, with the aid of
References: 1. F. L. Allen and J. Franck,Arch. Biochern. Biophys. 58.5 10 (1955). 2. C. P. Whittingham and P. M. Bishop, In Photosynthetic Mechanisms in Green Planrs, Publ. 1145, p 3. P. Joliot, Biochirn. Biophys. Acta 102, 1 16 (1965). 4. P. Joliot, Phorochern. Photobiol. 8,45 1 ( 1968). 5. P. Joliot, G . Barbieri and R. Chabaud, Photochern. Photobiol. 10,309 ( 1969). 6. P. Joliot and A. Joliot, Biochirn. Biophys. Acta 153,625 ( 1968). 8. G. M. Cheniae and 1. Martin, Biochirn.Biophys.Acta 197,219 (1970). 9. B. Forbush and B. Kok, Eiochirn. Biophys. Acta 162,253 (1968). 1 1. H. T. Witt, B. Skerra and J. Vater, In Currents in Photosynthesis Donker, Rotterdam ( 1966).