Genomic and experimental studies of the N. pharaonis electron transport chain. (A) The electron transport chain profile for several respiratory archaea displays subunits (squares) of respiratory complexes (boxes I–IV). These subunits are often encoded adjacently in the archaeal genomes (straight connections) and can be fused to each other (curved connections). The proposed electron flow between respiratory complexes is indicated by arrows. Complexes, which have been characterized experimentally, are indicated in blue, and protein-sequenced subunits of isolated complexes are yellow. The profile for Sulfolobus acidocaldarius (Sa) was established by complementation with genetic data from the completely sequenced Sulfolobus solfataricus (Ss) (asterisks). Menaquinone (MQ), caldariellaquinone (CQ), halocyanin (Hcy), and sulfocyanin (Scy) are shown or predicted to function as mobile carriers in archaeal respiratory chains. Homologs to complex I subunits have been found in archaeal genomes, but genes encoding the NADH acceptor module are missing. A functional NADH-dehydrogenating complex I has been experimentally excluded for three species (red). Instead, it is replaced by NADH dehydrogenase type II, which is not capable of proton translocation. (B,C) Oxidative and photo-phosphorylation processes in N. pharaonis cells were investigated through measurements of ATP levels (upper curves, mean values with error bars from triplicates) and extracellular pH (lower curves, continuous recording at a rate of 10/sec) in the (B) absence or (C) presence of the protonophore CCCP (0.2 mM). The effects (ON: above curve arrow, OFF: below curve arrow) of light (hν, λ > 515 nm, 32 mW/cm2) and aeration (O2) were determined. All experiments were performed at pH 8.1. Vertical scaling bars indicate ATP level and amount of proton uptake, whereas horizontal scaling bars indicate a 10-min time interval.
