ABSTRACT
Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption∕fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Qx state, but has almost no effect on the Qy state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Qx or Qy state. By comparing the kinetic traces of transient absorption, ground-state beaching, and stimulated emission after excitation to the Qx or Qy state, we showed that the Qx state was substantially incorporated in the ultrafast excited-state dynamics of bacteriochlorophyll a. Based on these observations, the lifetime of the Qx state was determined to be 50 and 70 fs for Mg- and Zn-bacteriochlorophyll a, respectively, indicating that the lifetime was influenced by the central metal atom due to the change of the energy gap between the Qx and Qy states.
Subject(s)
Bacteriochlorophyll A/chemistry , Magnesium/chemistry , Optical Phenomena , Zinc/chemistry , Absorption , Kinetics , Photochemical Processes , Spectrometry, FluorescenceABSTRACT
Ultrafast excited state dynamics of spirilloxanthin in solution and bound to the light-harvesting core antenna complexes from Rhodospirillum rubrum S1 were investigated by means of femtosecond pump-probe spectroscopic measurements. The previously proposed S∗ state of spirilloxanthin was clearly observed both in solution and bound to the light-harvesting core antenna complexes, while the lowest triplet excited state appeared only with spirilloxanthin bound to the protein complexes. Ultrafast formation of triplet spirilloxanthin bound to the protein complexes was observed upon excitation of either spirilloxanthin or bacteriochlorophyll-a. The anomalous reaction of the ultrafast triplet formation is discussed in terms of ultrafast energy transfer between spirilloxanthin and bacteriochlorophyll-a.
Subject(s)
Bacterial Proteins/chemistry , Solutions/chemistry , Energy Transfer , Kinetics , Photosynthesis , Rhodospirillum rubrum/chemistry , Xanthophylls/chemistrySubject(s)
Bacteriochlorophylls/metabolism , Light-Harvesting Protein Complexes/metabolism , Rhodospirillum rubrum/metabolism , Bacteriochlorophylls/chemistry , Energy Transfer , Light-Harvesting Protein Complexes/chemistry , Photosynthesis , Rhodospirillum rubrum/chemistry , Spectrometry, Fluorescence/methods , Time Factors , Xanthophylls/chemistry , Xanthophylls/metabolismABSTRACT
We previously showed that Asn-383 and Thr-1569 residues of p-loop regions in domains I and IV, respectively, of the puffer fish, Fugu pardialis, skeletal muscle Na(v) (fNa(v)1.4a), are anomalous to those of other species of TTX-sensitive Na(+) channels, where the aromatic residues of Phe or Tyr, and Gly are the counterparts [Yotsu-Yamashita, M., Nishimori, K., Nitanai, Y., Isemura, M., Sugimoto, A., Yasumoto, T., 2000. Binding properties of (3)H-PbTx-3 and (3)H-saxitoxin to brain membranes and to skeletal muscle membranes of puffer fish Fugu pardalis and the primary structure of a voltage-gated Na(+) channel alpha-subunit (fMNa1) from skeletal muscle of F. pardalis. Biochem. Biophys. Res. Commun. 267, 403-412]. The former was suggested to confer TTX resistance by using Y401N mutant of rNa(v)1.4 [Venkatesh, V., Lu, S.Q., Dandona, N., See, S.L., Benner, S., Soong, T.W., 2005. Genetic basis of tetrodotoxin resistance in pufferfishes. Curr. Biol. 15, 2069-2072]. The latter function remained to be elucidated. Thus, we further explored the function of these two residues, electrophysiologically, by evaluating the K(d) (dissociation constants) values of TTX for F385N, F385A, F385Q, G1718T, and F385N/G1718T mutants of rNa(v)1.2a, transiently expressed in HEK-293 cells. F385N caused 3000-fold increase of the K(d), while G1718T and F385N/G1718T caused 2- and 3-fold increases compared with those of WT and F385N, respectively, suggesting that G1718T further enhanced TTX resistivity caused by F385N. The K(d) for F385A and F385Q were 2- and 11-fold larger than that of F385N, respectively, suggesting that the longer side chain in the non-aromatic amino acid residue causes the larger decrease of TTX sensitivity. Despite drastic changes in the K(d), the mutations at F385 caused only small changes in the k(off) from that of WT, suggesting that the K(d) for TTX receptors are mainly determined by the k(on).
