Kinetic Analysis of Nonphotochemical Quenching of Chlorophyll Fluorescence. 1. Isolated Chloroplasts
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- 作者：Alexander V. Ruban ; Mark Wentworth ; and Peter Horton
- 刊名：Biochemistry
- 出版年：2001
- 出版时间：August 21, 2001
- 年：2001
- 卷：40
- 期：33
- 页码：9896 - 9901
- 全文大小：59K
- 年卷期：v.40,no.33(August 21, 2001)
- ISSN：1520-4995
文摘
Nonphotochemical quenching of chlorophyll fluorescence in plants is indicative of a processthat dissipates excess excitation energy from the light-harvesting antenna of photosystem II. The majorfraction of quenching is obligatorily dependent upon the thylakoid 
pH and is regulated by the de-epoxidation state of the xanthophyll cycle carotenoids associated with the light-harvesting complexes.Basic principles of enzyme kinetics have been used to investigate this process in isolated chloroplasts.The extent of quenching was titrated against the estimated thylakoid lumen pH, and a sigmoidal relationshipwas obtained with a Hill coefficient of 4.5 and a pK of 4.7. Upon de-epoxidation, these parameters changedto 1.6 and 5.7, respectively. Antimycin A suppressed quenching, increasing the Hill coefficient and reducingthe pK. The rate of induction of quenching fitted second-order kinetics with respect to illumination time,and the rate constant was dependent upon the pH, the de-epoxidation state, the presence of antimycin,and also the presence of dibucaine, a quenching enhancer. All these data are consistent with the notionthat quenching is caused by a conformational transition in a chloroplast thylakoid protein; this transitionshows cooperativity with respect to proton binding, and is controlled by de-epoxidation state and variousexogenous reagents.
pH and is regulated by the de-epoxidation state of the xanthophyll cycle carotenoids associated with the light-harvesting complexes.Basic principles of enzyme kinetics have been used to investigate this process in isolated chloroplasts.The extent of quenching was titrated against the estimated thylakoid lumen pH, and a sigmoidal relationshipwas obtained with a Hill coefficient of 4.5 and a pK of 4.7. Upon de-epoxidation, these parameters changedto 1.6 and 5.7, respectively. Antimycin A suppressed quenching, increasing the Hill coefficient and reducingthe pK. The rate of induction of quenching fitted second-order kinetics with respect to illumination time,and the rate constant was dependent upon the pH, the de-epoxidation state, the presence of antimycin,and also the presence of dibucaine, a quenching enhancer. All these data are consistent with the notionthat quenching is caused by a conformational transition in a chloroplast thylakoid protein; this transitionshows cooperativity with respect to proton binding, and is controlled by de-epoxidation state and variousexogenous reagents.