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Biomedical subjects
W B Whitten
Publications and source records attributed to W B Whitten.
Seven-fold exciton splitting of the 810-nm band in bacteriochlorophyll A-proteins from green photosynthetic bacteria.
We report comparative absorbance and fourth derivative absorbance spectra of two different bacteriochlorophyll a-proteins at 5 K in each of two different cryogenic solvent mixtures. In previous studies at 5 K each protein was observed in only one of these mixtures (not the same one). For the protein from Prosthecochloris aestuarii strain 2K, whose structure is known, the solvent effect is relatively small; for the protein from Chlorobium limicola f. sp. thiosulfatophilum strain 6230 (Tassajara), the effect is much more pronounced. From these results together with earlier results at 300 K, we conclude there may be slight conformational differences of the Prosthecochloris protein between the crystalline form used for X-ray diffraction studies and that in a cryogenic solvent. By comparing spectral features of the two proteins in the same solvent, we are able for the first time to assign all seven of the expected exciton levels in each protein. These occur at 793, 801, 806, 810, 814, 819, and 825 nm in the Prosthecochloris protein, and at 793, 802, 806, 810, 816, 820, and 823 nm in the Chlorobium protein.
Bacteria↗
Linear dichroism of electric field oriented bacteriochlorophyll alpha-protein from green photosynthetic bacteria.
Bacteriochlorophyll alpha-protein from Prosthecochloris aestuarii strain 2K was oriented in a pulsed electric field. The room temperature linear dichroism spectrum of the oriented protein in the Qy region of the bacteriochlorophyll alpha absorption exhibits a single asymmetrical peak at 813 nm with a shoulder extending to the blue. The approximately equal 12 nm fullwidth of the linear dichroism peak is only about half that of the 300 K absorption spectrum. The linear dichroism at 813 nm was not saturated at field strengths of up to 15 kV/cm. The time dependence of the linear dichroism suggests that the orienting particles are aggregates of at least some tens of bacteriochlorophyll alpha-protein trimers. The linear dichroism peak coincides in wavelength with the 813-nm peak of the 300 K, 4th derivative absorption spectrum of the protein and is therefore attributed to the bacteriochlorophyll a Qy exciton transition observed in absorption at the same wavelength.
Bacteria↗
Derivative absorption spectroscopy from 5--300 K of Prosthecochloris aestuarii.
Absorption spectra of the bacteriochlorophyll a-protein from Prosthecochloris aesturaii were measured at temperatures from 2.9 to 300 K. Fourth and eight derivatives of the spectra were calculated from the digital data. From an analysis of 34 scans taken from 750 to 850 nm at 5 K, and 130 scans taken from 822 to 838 nm, we find evidence for nine peaks, six of which are probably 0--0 excitonic and three probably higher vibronic features. The major peaks are resolved in the derivative spectra to 300 K, and all shift with temperature by less than 1 nm compared to their 5 K positions, except for the 825 nm peak which shifts about 2 nm. The most prominent fourth derivative peak at 300 K shifts from 812.9 nm in the standard buffer solution to 814.1 nm in the cryogenic solution in which our low temperature measurements were made. We conclude that the conformation of the protein at 5 K is essentially the same as at 300 K.
Bacteria↗