Solvation effect of bacteriochlorophyll excitons in light-harvesting complex LH2.

We have characterized the influence of the protein environment on the spectral properties of the bacteriochlorophyll (Bchl) molecules of the peripheral light-harvesting (or LH2) complex from Rhodobacter sphaeroides. The spectral density functions of the pigments responsible for the 800 and 850 nm electronic transitions were determined from the temperature dependence of the Bchl absorption spectra in different environments (detergent micelles and native membranes). The spectral density function is virtually independent of the hydrophobic support that the protein experiences. The reorganization energy for the B850 Bchls is 220 cm(-1), which is almost twice that of the B800 Bchls, and its Huang-Rhys factor reaches 8.4. Around the transition point temperature, and at higher temperatures, both the static spectral inhomogeneity and the resonance interactions become temperature-dependent. The inhomogeneous distribution function of the transitions exhibits less temperature dependence when LH2 is embedded in membranes, suggesting that the lipid phase protects the protein. However, the temperature dependence of the fluorescence spectra of LH2 cannot be fitted using the same parameters determined from the analysis of the absorption spectra. Correct fitting requires the lowest exciton states to be additionally shifted to the red, suggesting the reorganization of the exciton spectrum.

Temperature broadening of LH2 absorption in glycerol solution.

In order to determine the relationship between the pigment-protein and the pigment-pigment interactions, the measurements of absorption spectra of the peripheral light-harvesting complex LH2 from the purple bacteria Rhodobacter sphaeroides solvated in glycerol/buffer solution were carried out in a wide temperature range, from 4 to 250 K. The SDFs used for simulating the temperature dependence of B800 and B850 bands were determined in a parametric form. To fit experimental spectra the overall exciton-phonon coupling had to be assumed to be weak for B850 (lambda/2V approximately 0.3, where lambda is the reorganization energy and V is the nearest-neighbor dipole-dipole coupling for bacteriochlorophylls). At physiological temperatures the intermediate nuclear bath dynamics compares with the magnitude of energy gap fluctuations. Slower dynamics with kappa approximately 0.39, where kappa is the ratio of the nuclear relaxation rate and the line width parameter, determines the spectral shape of B850 whilst faster modulations characterize B800 (kappa approximately 2.39). The static disorder for the B800 band is relatively high with the characteristic value of the inhomogeneous bandwidth Gamma(inh) approximately 120 cm-1, while for the B850 band this value is almost equal to the dipole-dipole coupling strength (Gamma(inh) approximately 360 cm-1). It has been found that the LH2 absorption spectrum is likely to be influenced by the temperature dependence of the dielectric constant of the solution in the high temperature range, when the glycerol/buffer solution is in the liquid state.

Dates of onset of relapses and the duration of infection in induced tertian malaria with short and long incubation periods.

The course of induced tertian malaria has been studied in patients in psychoneurological hospitals in Moscow over a long period. Various strains of P. vivax were used to infect patients; the sporozoites were transmitted by Anopheles maculipennis atroparvus bred under laboratory conditions. There are marked differences between the dates of onset of relapses, reckoned from the primary manifestations of the disease, in patients developing malaria after long and short incubation periods. P. vivax strains which have a short incubation period are characterized by producing in patients a series of relapses following a long latent period; strains with a long incubation period are characterized by the occurrence of relapses during the first 3 months after the end of the primary series of attacks. However, some P. vivax strains give rise to both types of relapse, depending on the incubation period. In any event, the duration of the disease does not, as a rule, exceed 2 years, including the incubation period. The number of mosquitos (and hence the number of sporozoites) used to infect a patient does not have any noticeable effect on the number and frequency of relapses. In short-incubation tertian malaria, the use of quinocide during the period of treatment of the primary manifestations greatly reduced the number of relapses; in long-incubation tertian malaria similarly treated with quinocide, no relapses occurred.