Ammonia-induced Structural Changes of the Oxygen-Evolving Complex in Photosystem II as Revealed by Light-Induced FTIR Difference Spectroscopy


Ya-Wen Feng#, Chiu-Ming Wang#, Shyue-Chu Ke and Hsiu-An Chu#

# Institute of Botany, Academia Sinica, Nan-Kang, Taipei 11529, Taiwan

Department of Physics, National Dong Hwa University, Hualien, 97401, Taiwan


The catalytic site of photosystem II (PSII) reaction centers contains a (Mn)4 cluster that interacts closely with a redox-active tyrosine residue known as YZ.  The (Mn)4 cluster accumulates oxidizing equivalents in response to photoinduced electron transfer reactions within PSII, then catalyzes the oxidation of two molecules of water, release one molecule of O2 as a by-product.  The progression of the oxygen-evolving complex (OEC) goes through a cycle of five intermediates states, labeled as the Sn state (n = 0-4), where n denotes the number of stored equivalents.  The detailed molecular structure and mechanism of OEC in PSII are still not clear.  NH3 is an analog of substrate H2O and also an inhibitor of water oxidation.  By combining FTIR difference techniques with isotopic labeling methods, we are studying the interaction of NH3 with the OEC.  We found that the S2 state carboxylate mode in the S2QA-/S1QA spectrum is affected upon the NH3 treatment but the corresponding S1 carboxylate mode at 1402 cm-1 is not affected.  Our results suggest that NH3 is not bound until the formation of the S2 state.  In addition, we found that CH3NH2 has a small but clear effect on the S2QA-/S1QA FTIR difference spectrum.  Our results showed that the effects of amines on the S2QA-/S1QA FTIR difference spectrum of PSII are sterically selective for small amines.  The correlations between NH3-modified FTIR spectra and the NH3-modified g=2 multiline EPR signal will be presented.




Fluoride substitution in the Mn cluster from photosystem II: FTIR studies

Cheng-Hao Fang#,‡, Keejong Chang and Hsiu-An Chu#

# Institute of Botany, Academia Sinica, Nan-Kang, Taipei, 11529, Taiwan

Department of Chemistry, Soochow University, Shih Lin, Taipei, Taiwan


Fluoride inhibits the activity of the oxygen-evolving complex (OEC) of photosystem II (PSII).  It has been suggested that fluoride compete the chloride binding site in PSII.  However, the exact roles of chloride and fluoride ions on the function of the PSII/OEC are still not clear.  Light-induced Fourier transform infrared difference spectroscopy has been applied to studies of fluoride effects on the PSII/OEC.  We found that fluoride induced characteristic spectral changes in the region of the amide I (1700-1600 cm-1) and the symmetric carboxylate stretching modes (1450-1300 cm-1) of the S2QA-/S1QA FTIR difference spectra of PSII.  The symmetric carboxylate stretching modes at ~1400 and 1365 cm-1 in the S2QA-/S1QA spectrum of the controlled samples were diminished in that of Fluoride-treated samples.  These two carboxylate modes have been assigned to a Mn-ligating carboxylate whose coordination mode changes from bridging or chelating to unidentae ligation during the S1 to S2 transition [Noguchi, T., Ono, T., and Inoue, Y. (1995) Biochim Biophys Acta 1228, 189-200; Kimura, Y. and Ono, T.-A. (2001) Biochemistry 40, 14061-14068].  Therefore, our results show that fluoride-induced significant structural changes of the OEC in both the S1 and S2 state.  In addition, our results also showed that chloride ions restore the fluoride-induced spectral changes of the S2QA-/S1QA spectrum of PSII.  Our results support that fluoride is competing with the chloride binding site in PS II.  The possible role of chloride in the oxygen-evolving mechanism of PS II will be discussed.




Monitoring Transdermal delivery of quantum dots using multiphoton fluorescence microscopy

Wen Lo 1*, Tso Chien-Hsin 1, Pei-Yu Huang2, Chan-Long Chen2, Chia-Chun Chen2, Sun-Jan Lin3,

Shiou-Hwa Jee3, Chen-Yuan Dong 1

1Department of Physics, National Taiwan University, No.1 Roosevelt Road Sec. 4, Taipei, 106, Taiwan

2 Department of Chemistry, National Taiwan Normal University, No. 88, Sec. 4,

Ting-Chow Rd., Taipei, Taiwan, 116.

3 National Taiwan University Hospital, No.7, Chung San South Road, Taipei, 100, Taiwan and

National Taiwan University, College of Medicine., No.1, Ren-Ai Rd, 1st Section, Taipei, 100, Taiwan


 Luminescent quantum dots (QDs) are attractive fluorescent probes in bioimaging application. Broad excitation spectrum, narrow and tunable emission spectrum, high photochemical stability and chemical modifiability are among the desirable properties of QDs. In this work, we investigate the feasibility of administering QDs (7 nm in size) through transdermal delivery pathway using multiphoton fluorescence imaging. Our results show that QDs of this size range can be effectively delivered through intercellular pathways using the chemical enhancer oleic acid. This work has implications for understanding the transport of important biological macromolecules.

Our experiments infer two important results. First QDs can hardly transport into skin without the chemical enhancer oleic acid. Furthermore, QDs deliver primarily through intercellular pathways. In contrast, fluoresein molecules deliver through both intercellular and intracellular region.

Our results imply that the size of nanoparticles may dominate the nature of transdermal transport mechanism and in the future, we plan to investigate the mechanism by manipulating the size of nanoparticles and their surface chemistry.