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Gel-electrophoretic assay revealed that the photosynthetic reaction center (RC) of Chromatium minutissimum, in contrast to the well-known RC Rhodopseudomonas viridis, consists of five rather than four subunits with molecular masses of 37, 34, 25, 19, and 17 kDa. The 37- and 19-kDa subunits are stained with tetramethylbenzidine for the cytochrome c hemes. Absorption spectra show that the concentration of reduced cytochromes in the C. minutissimum RC poised at redox potential of -150 mV (fully reduced pool of hemes) is about three times more than in the C. minutissimum RC poised at redox potential of +260 mV (only high-potential hemes are reduced). The results of redox titration of absorption changes at the cytochrome c alpha-band are most appropriately approximated by a six-component theoretical curve with the midpoint potentials of Em1 = 390 mV, Em2 = 320 mV, Em3 = 210 mV, Em4 = 100 mV, Em5 = 20 mV, and Em6 = -50 mV. Possible functions of the cytochromes with the midpoint potentials 210 and 100 mV, which have not been found in purple bacteria before, are discussed.

The riboprinting technique (restriction fragment length polymorphism [RFLP] analysis of PCR-amplified ribosomal DNA) was used to study five strains representing three species of the genus Chromatium. An RFLP analysis following digestion of the amplified small-subunit ribosomal DNA with 25 restriction enzymes revealed that the patterns obtained for all strains of Chromatium vinosum were identical. Chromatium gracile was different from C. vinosum with seven enzymes. On the other hand, Chromatium minutissimum produced the same patterns as C. vinosum with all enzymes, indicating that these organisms have a high degree of similarity. An RFLP analysis of the PCR-amplified spacer sequence between the 16S and 23S ribosomal DNAs gave similar results except that there was a larger number of differences between C. gracile and the other organisms examined.

The picosecond dynamics of excitations in the isolated B800-850 light-harvesting complex of the purple sulfur bacterium Chromatium minutissimum has been studied using picosecond fluorescence spectrochronography. A short-lived component of about 20 ps lifetime has been found at 77K at the short wavelength part of the B850 fluorescence spectrum similar to that previously described for the core antenna bacteriochlorophyll band B880 of Rhodospirillum rubrum. Evidence has been presented indicating that this component is likely to reflect excitation energy relaxation step(s) involving both photoexcited bacteriochlorophyll and the protein environment. A new kinetic scheme of excitation transfer from the peripheral antenna to the photoreceptor units in purple bacteria is suggested which takes into account these findings.

Spatial relationships between difterent pigment-protein complexes in the membranes of the purple photosynthetic bacterium, Chromatium minutissimum , have been studied. The possibility of restoring the function of efficient excitation energy transfer from bacteriochlorephyll molecules to the reaction centers in the system of soybean liposomes, reconstituted with pigment-protein complexes B800-850 and B890-RC from C. minutissimum , has been explored. The chemical cross-linking method, together with stationary and picosecond spectrally resolved fluoresence measurements were employed. It has been shown that after the incorporation of the complexes into the liposame membranes conditions for directed excitation energy transfer from the light-harvesting pigments to the reaction centers are created, which are less optimal, however, than those in the native state. Possible reasons are considered.

Native and carotenoid-depleted peripheral purple bacterial light-harvesting complex (LH2) were investigated by simultaneous two-photon excited (between 1300–1500 nm) fluorescence (TPF). TPF results from direct bacteriochlorophyll excitation in both samples. The spectral position of the 2A g − state of rhodopsin is indicated by a diminuition of the bacteriochlorophyll TPF in native LH2. In conclusion, comparison to carotenoid-depleted samples is a conditio sine qua non for unambiguous interpretation of similar experiments.