Resting state of respiratory Complex I from Escherichia coli

Respiratory Complex I from Escherichia coli may exist in two states, resting (R) and active (A). The conversion from the R‐ to A‐forms occurs spontaneously upon turnover. The fast resting‐to‐active (R/A) transition of membrane‐bound and purified Complex I was studied with the stopped‐flow technique by following NADH oxidation either by absorption decay at 340 nm or using the fluorescent pH indicator, trisodium 8‐hydroxypyrene‐1,3,6‐trisulfonate (pyranine). The R/A transition of Complex I from E. coli occurs upon its turnover in a time interval of ~ 1.5 s. Comparisons between the bacterial Complex I R/A transition and the active/deactive transition of mitochondrial Complex I are discussed.