Cytochrome b6 from isolated cytochrome b6f complexes Evidence for two spectral forms with different midpoint potentials

AbstractCytochrome b6 from spinach chloroplasts (either within the purified cytochrome b6f complex, or in its isolated form) exhibits two spectral species, which correspond to two midpoint potentials. This can be demonstrated by low temperature difference spectroscopy at fixed redox potentials. The high potential form of cytochrome b6 has a split α-peak at 557.5 and 561.5 nm, the low potential form has a symmetrical α-peak at 560.5 nm. Similar results were obtained with cytochrome b6 in the isolated cytochrome b6f complex from the cyanobacterium Anabaena variabilis

The atp2 operon of the green bacterium Chlorobium limicola

The operon (atp2) encoding the β and ε{lunate} subunits of F-ATPase from Chlorobium limicola was cloned and sequenced. In contrast with purple bacteria these genes are arranged in a separate operon similar to the cyanobacteria. The operon terminates with a pronounced stem-loop structure. About 0.8 kb upstream of the β subunit a gene encoding the enzyme phosphoenolpyruvate carboxykinase was identified. This gene is transcribed in the opposite direction of the atp2 operon and also ends with a stem-loop structure. These genes of green bacteria are among the first to be sequenced, and therefore the genetic distance between these genes and corresponding genes from other bacteria and eukaryotes was studied. Even though the operon structure resembles that of cyanobacteria, the evolutionary tree compiled from these data places the chlorobium gene close to purple bacteria. Chlorobium limicola β and ε{lunate} subunits complemented Escherichia coli mutants defective in the corresponding subunits, indicating that the hybrid enzyme formed from subunits of the two bacteria is active in ATP synthesis