The nature of a pgiment-protein complex excreted from mutants of Rhodopseudomonas sphaeroides.

Pigment-protein complexes excreted from three bacteriochlorophyll-less mutants (mutants 8, 8-29, and 8-47) of Rhodopseudomonas sphaeroides have been isolated and purified. In the absence of detergents the complexes remained in an aggregated state, but were disaggregated by 0.2% Triron X-100. Sepharose 6B gel filtration indicated that the disaggregated complex from each of the mutants had a particle weight of about 165000, and contained 30 +/- 3% protein. This complex was further dissociated by 1% sodium dodecyl sulfate. Sephadex G-100 gel filtration now indicated that the majority of the protein was present as a small polypeptide with a molecular weight of about 9000. The pigment-protein complex from one of the mutants was treated with a bacteriochlorophyll extract. The bacteriochlorophyll was converted to bacteriopheophytin and became bound to the protein, replacing the endogenous tetrapyrrole (a bacteriocholorophyll precursor). The red absorption maximum of the bacteriopheophytin was shifted during this process to 840-865 nm. These properties are consistent with the possibility that the pigment-protein complexes contain a protein normally associated with light-harvesting bacteriochlorophyll in the wide-type strain.