Accelerated Publications Femtosecond Transient Absorption Study of Carotenoid to Chlorophyll Energy Transfer in the Light-Harvesting Complex II of Photosystem II ² James P. Connelly, ‡ Marc G. Mu ¨ller, ‡ Roberto Bassi, § Roberta Croce, § and Alfred R. Holzwarth* ,‡ Max-Planck-Institut fu ¨ r Strahlenchemie, Stiftstrasse 34-36, D-45470 Mu ¨ lheim an der Ruhr, Germany, and Biotechnologie Vegetali, UniVersita ` di Verona, Strada Le Grazie, Verona I-37100, Italy ReceiVed October 1, 1996; ReVised Manuscript ReceiVed NoVember 13, 1996 X ABSTRACT: Singlet energy transfer between the carotenoids (Cars) and chlorophylls (Chls) in the light- harvesting complex II (LHC II) from higher plants has been studied using ultrafast transient absorption spectroscopy by exciting the Cars directly in the 475-515 nm wavelength range. LHC II trimers from Arabidopsis thaliana with well-defined Car compositions have been used. From HPLC, the wild type (WT) monomer contains two luteins (Ls), one neoxanthin (N), and a trace of violaxanthin (V) per 12 Chls. The ABA-3 mutant contains 1.4 Ls and 0.6 zeaxanthin (Z) per monomer. Though exploitation of the difference in Car constitution and exciting the WT at 475 and 490 nm, and the ABA-3 mutant at 490 and 515 nm, the different Car contributions to energy transfer have been probed. Evidence for energy transfer mainly from the Car to Chl b is observed in the WT. In the mutant, additional transfer from Car to Chl a correlates with the presence of Z. The results imply predominant energy transfer from the central Ls to Chl b which requires a modification of the currently accepted arrangement of Chl pigments in LHC II. As the most abundant and outermost antenna of photo- system (PS) II, light-harvesting complex (LHC) 1 II is involved in absorption and energy transfer mainly by means of chlorophyll (Chl) that paves the excitation transfer route to the reaction center (Jennings et al., 1996). Carotenoids (Cars) are also present and fulfill several functions (Frank & Cogdell, 1996). Nonphotochemical quenching mecha- nisms that control the efficiency of PS II (Horton et al., 1996; Ruban et al., 1996) are known to involve the xanthophyll cycle Cars, although the location of the most significant quenching processes appears to be predominantly associated with the minor antennas, i.e. CP 26 and 29 (Bassi et al., 1993; Bergantino et al., 1995). Rather, the Cars associated with LHC II probably serve both to prevent the formation of the Chl triplet state that can react with oxygen to form the damaging singlet oxygen (Peterman et al., 1995) and as antennas absorbing in the blue green spectral region and transferring singlet excitation to the Chls (Frank & Cogdell, 1996). The Cars are also vital for stabilizing the structure of LHC II, as demonstrated by the need for them in reconstituting LHC II (Paulsen, 1995). The spectral properties of carotenoids, typical of those found in antenna complexes, have been studied quite ² This work was performed within the European Union HCM network (Contract CT940619) and was also supported in part by the Deutsche Forschungsgemeinschaft SFB 189, Heinrich-Heine-Universita ¨t Du ¨sseldorf, and the Max-Planck-Institut fu ¨r Strahlenchemie, Mu ¨lheim an der Ruhr. * To whom correspondence should be addressed. E-mail: holzwarth@mpi-muelheim.mpg.de. ‡ Max-Planck-Institut fu ¨r Strahlenchemie. § Universita ` di Verona. X Abstract published in AdVance ACS Abstracts, December 15, 1996. 1 Abbreviations: A, antheraxanthin; Car, carotenoid; Chl a and b, chlorophyll a and b, respectively; CP 24, 26, and 29, chlorophyll- protein complexes of PS II; DADS, decay-associated absorption difference spectra; DM, n-dodecyl -maltoside; ESA, excited state absorption; ET, energy transfer; HPLC, high-performance liquid chromatography; IEF, isoelectric focusing; L, lutein; LHC II, light- harvesting complex II; N, neoxanthin; PAGE, polyacrylamide gel electrophoresis; V, violaxanthin; Z, zeaxanthin. © Copyright 1997 by the American Chemical Society Volume 36, Number 2 January 14, 1997 S0006-2960(96)02467-1 CCC: $14.00 © 1997 American Chemical Society