Experimental evidence of oligomeric organization of antenna bacteriochlorophyll c in green bacterium Chloroflexus aurantiacus by spectral hole burning

AbstractSpectral hole burning has been used to prove experimentally the existence in natural antenna of one of the predicted structural optimizing factors — antenna pigment oligomerization [J. Theor. Biol. 140 (1989) 167]—ensuring high efficiency of excitation energy transfer from antenna to reaction center, This point has been examined for the chlorosomal antenna of green bacterium Chloroflexus auranticus by hole burning in fluorescence excitation and emission spectra of intact cells at 1.8 K. The persistent hole spectra have been found to be consistent with a strongly exciton-coupled bacteriochloraphyll c (BChl c) chromophore system. The lowest exciton state of BChl c oligomers has been direclly detected and separated as the lowest energy inhomogeneously broadened band (FWHM ∼90 cm−1, position of maximum, at ∼752 nm) from the near-infrared BChl c band (FWHM ∼350 cm−1, position or maximum, at ∼74 nm) of 1.8 K excitation spectrum

Spectral hole burning study of intact cells of green bacterium Chlorobium limicola

AbstractSpectral hole burning studies of intact cells of the green bacterium, Chlorobium limicola, have proven that the Qy-absorption system of antenna bacteriochlorophyll c (BChl c) should be interpreted in terms of the delocalized exciton level structure of an oligomer. For the first time the 0-0 band of the lowest exciton state of BChl c oligomers has been directly detected as the lowest energy inhomogeneously broadened band (FWHM −100 cm−1; position of maximum, at ~774 nm) of the near-infrared BChl c band of 1.8K excitation spectrum (FWHM = 830 cm−1; position of maximum, at 751 nm)

Excitation energy transfer in chlorosomes of green bacteria: theoretical and experimental studies.

A theory of excitation energy transfer within the chlorosomal antennae of green bacteria has been developed for an exciton model of aggregation of bacteriochlorophyll (BChl) c (d or e). This model of six exciton-coupled BChl chains with low packing density, approximating that in vivo, and interchain distances of approximately 2 nm was generated to yield the key spectral features found in natural antennae, i.e., the exciton level structure revealed by spectral hole burning experiments and polarization of all the levels parallel to the long axis of the chlorosome. With picosecond fluorescence spectroscopy it was demonstrated that the theory explains the antenna-size-dependent kinetics of fluorescence decay in chlorosomal antenna, measured for intact cells of different cultures of the green bacterium C. aurantiacus, with different chlorosomal antenna size determined by electron microscopic examination of the ultrathin sections of the cells. The data suggest a possible mechanism of excitation energy transfer within the chlorosome that implies the formation of a cylindrical exciton, delocalized over a tubular aggregate of BChl c chains, and Forster-type transfer of such a cylindrical exciton between the nearest tubular BChl c aggregates as well as to BChl a of the baseplate

Sex differences in the development of diabetes in mice with deleted Wolframin (Wfs1) gene-an animal model for Wolfram syndrome: O/5/FRI/03

Oral presentatio

Sex differences in the development of diabetes in mice with deleted wolframin (Wfs1) gene

Wolfram syndrome, caused by mutations in the wolframin (Wfs1) gene, is characterised by juvenile-onset diabetes mellitus, progressive optic atrophy, diabetes insipidus and deafness. Diabetes tend to start earlier in boys. This study investigated sex differences in longitudinal changes in blood glucose concentration (BGC) in wolframin-deficient mice (Wfs1KO) and compared their plasma proinsulin and insulin levels with those of wild-type (wt) mice. Non-fasting BGC was measured weekly in 42 (21 males) mice from both groups at nine weeks of age. An intraperitoneal glucose tolerance test (IPGTT) was conducted at the 30th week and plasma insulin, c-peptide and proinsulin levels were measured at the 32nd week. At the 32nd week, Wfs1KO males had increased BGC compared to wt males (9.40±0.60 mmol/l vs. 7.91±0.20 mmol/l; p<0.05). The opposite tendency was seen in females. Both male and female Wfs1KO mice had impaired glucose tolerance on IPGTT. Wfs1KO males had significantly lower mean plasma insulin levels than wt males (57.78±1.80 ng/ml vs. 69.42±3.06 ng/ml; p<0.01) and Wfs1KO females (70.30±4.42 ng/ml; p<0.05). Wfs1KO males had a higher proinsulin/insulin ratio than wt males (0.09±0.02 vs. 0.05±0.01; p=0.05) and Wfs1KO females (0.04±0.01; p<0.05). Plasma c-peptide levels in males were lower in Wfs1KO males (mean 55.3±14.0 pg/ml vs. 112.7±21.9 pg/ml; p<0.05). Male Wfs1KO mice had a greater risk of developing diabetes than female Wfs1KO mice. Low plasma insulin concentration with an increased proinsulin/insulin ratio in Wfs1KO males indicates possible disturbances in converting proinsulin to insulin which in long-term may lead to insulin deficiency. Further investigation is needed to clarify the mechanism for the sex differences in the development of diabetes in Wolfram syndrome

Energy transfer in ethane-bisporphyrins studied by fluorescence line narrowing and spectral hole burning

The quasi-line fluorescence excitation spectrum of 1,2-bis (2,3,7,8,12,13,17,18-octaethyl-21H,23 H-porphino) ethane at 4.8 K consists of two subbands with the splitting mean value of 51cm⁻¹, that are ascribed to the donor and the acceptor half of the homodimer. The donor's fluorescence is quenched by an efficient energy transfer to the acceptor. The energy transfer rate of 10¹¹ s⁻¹, determined by spectral hole burning, has been compared with the calculated value and a conclusion of nonconsistency with the Forster energy transfer mechanism has been drawn