Estimation of the H+/H- ratio of the reaction catalysed by the nicotinamide nucleotide transhydrogenase in chromatophores from over-expressing strains of Rhodospirillum rubrum and in liposomes inlaid with the purified bovine enzyme.
Two strains of Rhodospirillum rubrum were constructed in which, by a gene dosage effect, the transhydrogenase activity of isolated chromatophores was increased 7-10-fold and 15-20-fold, respectively. The H+/H- ratio (the ratio of protons translocated per hydride ion equivalent transferred from NADPH to an NAD+ analogue, acetyl pyridine adenine dinucleotide), determined by a spectroscopic technique, was approximately 1.0 for chromatophores from the over-expressing strains, but was only approximately 0.6 for wild-type chromatophores. Highly-coupled proteoliposomes were prepared containing purified transhydrogenase from beef-heart mitochondria. Using the same technique, the H+/H- ratio was close to 1.0 for these proteoliposomes. It is suggested that the mechanistic H+/H- ratio is indeed unity, but that a low ratio is obtained in wild-type chromatophores because of inhomogeneity in the vesicle population.
Bizouarn
T
T
School of Biochemistry, University of Birmingham, Edgbaston, UK.
Sazanov
L A
LA
Aubourg
S
S
Jackson
J B
JB
D000818:Animals; D020130:Bacterial Chromatophores / Q000201:enzymology*; D002417:Cattle; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D008081:Liposomes; D008929:Mitochondria, Heart / Q000201:enzymology; D009250:NADP Transhydrogenases / Q000737:chemistry / Q000378:metabolism*; D010957:Plasmids; D011522:Protons; D012247:Rhodospirillum rubrum / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure
D008081:Liposomes; D011522:Protons; D009250:NADP Transhydrogenases