Search

Chlorophylls provide the basis for photosynthesis and thereby most life on Earth. Besides their involvement in primary charge separation in the reaction center, they serve as light-harvesting and light-sensing pigments, they also have additional functions, e.g., in inter-system electron transfer. Chlorophylls also have a wealth of applications in basic science, medicine, as colorants and, possibly, in optoelectronics. Considering that there has been more than 200 years of chlorophyll research, one would think that all has been said on these pigments. However, the opposite is true: ongoing research evidenced in this Special Issue brings together current work on chlorophylls and on their carotenoid counterparts. These introductory notes give a very brief and in part personal account of the history of chlorophyll research and applications, before concluding with a snapshot of this year’s publications.

The 8 linker-polypeptides from the cyanobacterium Mastigocladus laminosus were examined by comparative amino-acid sequence analysis for the predicted domain structure reported in the literatur (Glauser 1991, Esteban 1993) in detail using split sequences for the rod, rod-core and for the repeats from the core-membrane linker-polypeptide (Lcm127.6). This analysis gives two distinct domains, where domain 1 (∼ 22 kDa, identity between 31 and 70%) is present in the N-terminal two thirds of the class II linkers (∼ 30 kDa) and in the repeats of the Lcm127.6, and domain 2 (∼ 10 kDa, identity between 28 and 41%) in the C-terminal part of the class II rod linkers (Lr31.5 and Lr32.5) and in the two capping linkers (Lc7.7 and Lr8.2). Based on these data, X-ray structure analysis from phycobiliproteins and proteolysis experiments, an interlocking model for the phycobilisome rod organization is proposed, with linkers protruding from one phycobilisome disk into the neighbouring one.

The reversible photochemistry of the α-subunit of phycoerythrocyanin (α-PEC) has been measured by low temperature absorption and circular dichroism in the range of 125K to 295 K. Below 185 K, the photochemistry is nearly silent; above 205 K, the photochemistry increases gradually without an indication of intermediates, and between 185 to 205K spectral changes in absorption and circular dichroism indicate an intermediate and/or changes in the interaction(s) between the chromophore and its environment.

Abstract  Single molecule spectroscopy was applied to study the optical properties of native and refolded peridinin–chlorophyll–protein (PCP) complexes. The native system is a trimer with six chlorophyll a (Chl a) molecules, while the refolded one contains two Chl a and resembles structurally and spectroscopically the PCP monomer. The fluorescence emission of single PCP complexes strongly broadens with increasing excitation power. Simultaneously, the distribution of fluorescence maximum frequencies is also broadened. These spectral changes are attributed to photoinduced conformational changes of the protein that influence the fluorescence of embedded chromophores. Comparison of fluorescence intensities measured for PCP complexes in two different solvents indicates that the native PCP trimers are preserved in EDTA Tris buffer, while in PVA polymer matrix only monomers are stable. [ABSTRACT FROM AUTHOR]

Abstract  The phycobilin: Cysteine-84-phycobiliprotein lyase, CpeS1, catalyzes phycocyanobilin (PCB) and phycoerythrobilin attachment to nearly all cysteine-84 (consensus sequence) binding sites of phycoerythrin, phycoerythrocyanin, phycocyanin and allophycocyanin (Zhao et al. (2007) Proc Natl Acad Sci 104:14300–14305). We now show that CpeS1 can bind PCB, as assayed by Ni2 chelating affinity chromatography. Binding is rapid, and the chromophore is bound in an extended conformation similar to that in phycobiliproteins but only poorly fluorescent. Upon addition of apo-biliproteins, the chromophore is transferred to the latter much slower (∼1 h), indicating that chromophorylated CpeS1 is an intermediate in the enzymatic reaction. In addition, imidazole is bound to PCB, as shown by mass spectroscopy of tryptic digests of the intermediate CpeS1–PCB complex. [ABSTRACT FROM AUTHOR]

Bacteriochlorophyll a and bacteriopheophytin a carry a stereochemically labile asymmetric carbon at position C13². The steric requirements of photosynthetic reaction centers from Rhodobacter sphaeroides R26 have been probed by exchange experiments with the respective epimeric 13²-hydroxylated pigments, in which epimerisation is blocked. (13²S)-13²-Hydroxy-bacteriochlorophyll a is accepted at both monomeric binding sites, BA,B, (13²S)-13²-hydroxy-bacteriopheophytin a exclusively at the inactive site HB. The orientation of the 13²-COOCH3 substituents in these pigments is the same as in the native (13²R)-bacteriochlorophylls and (13²R)-bacteriopheophytins. In no cases are the unnaturally configured 13²-hydroxylated (13²R)-epimers accepted, even if a large excess (> 95%) is offered. It is concluded that the three binding sites always require the 13²-COOCH3 group on the opposite side of the macrocycle (down) than the 17-propionic ester side chain (up). [ABSTRACT FROM AUTHOR]