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The gene (puhA) encoding the H subunit of the reaction center (RC) was deleted by site-directed interposon mutagenesis by using a kanamycin resistance cassette lacking transcriptional terminators to eliminate polar effects in both the wild-type strain Rhodospirillum rubrum S1 and the carotenoid-less strain R. rubrum G9. The puhA interposon mutants were incapable of photoheterotrophic growth but grew normally under aerobic chemoheterotrophic conditions. Absorption spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the RCs were absent. In minimal medium and also in modified medium containing succinate and fructose, the light-harvesting 1 complex (LH1) levels of the S1-derived mutants were about 70 to 100% of the wild-type levels in the same media. The correct assembly of LH1 in the membrane and the pigment-pigment interaction were confirmed by near-infrared circular dichroism spectroscopy. LH1 formation was almost absent when the carotenoid-less G9-derived puhA mutants were grown in standard minimal medium, suggesting that carotenoids may stabilize LH1. In the fructose-containing medium, however, the LH1 levels of the G9 mutants were 70 to 100% of the parental strain levels. Electron micrographs of thin sections of R. rubrum revealed photosynthetic membranes in all mutants grown in succinate-fructose medium. These studies indicate that the H subunit of the RC is necessary neither for maximal formation of LH1 nor for photosynthetic membrane formation but is essential for functional RC assembly.

The influence exerted on an integral membrane protein by its environment using the light-harvesting complex (LHI) of purple bacteria as a model, is studied. It is concluded that membrane environment significantly narrows the statistical distribution of conformational states available to the LH1 complex in comparison to the corresponding state distribution observed for the same detergent-solubilized protein.

A study on the possibility that the psg gene in Rhodospirillum rubrum contains a 3,4-desaturase and that its disruption produces nonnatural carotenoids is presented. The Rhodospirillum ST4 mutant with a single Tn5 lesion has been isolated wherein a latent branching of the biosynthetic pathway has been discovered. The unnatural carotenoids may have been produced by the incorporation of a cryptic branch in the linear pathway for spirilloxanthin biosynthesis. Results show that the ST4 mutant is a good system for studying the role of carotenoids in bacterial photosynthesis.

Rapid optical fiber-based spectroscopy accurately records the reflection and absorption spectra of single bacterial colonies. The fiber-optic spectroradiometer with diode array detection is capable of assessing at least 500 colonies per day. The accuracy of spectral measurements permits the determination of small changes in peak maxima. Reliable reflectance spectra are available within a range of 450-820 nm, and a transmission spectral range of 400-900 nm produces reliable peak intensities and absorption maxima.

A study was conducted on reconstitution strategies and conditions for optimizing the incorporation of the human placental transferring receptor (hTfR) into phospholipid bilayers using either gel filtration, dialysis or dilution. Excellent results were achieved when hTfR was dissolved with octylpolyoxyethylene, mixed with detergent-solubilized soy bean lecithin and reconstituted by slow dialysis. HTfR reconstitution caused the formation of long tubular structures proceeding from the vesicle surface.

The fluorescence spectroscopy technique is employed to study the initial binding process of the inner membrane insertase YidC with its substrate, the Pf3 coat protein. The results demonstrate the presence of a reversible and noncooperative binding between YidC and its substrate.