Growth Phase and the Number of Phosphorylation Sites in the Mitochondrial Electron Transport Chain of Acanthamoeba castellanii

SYNOPSIS. Mitochondria isolated from the soil ameba Acanthamoeba castellanii growing exponentially on complex medium have rotenone-insensitive oxygen uptake and ADP:O ratios which indicate the presence of only 2 phosphorylation sites in the electron transport chain. Stationary phase amebae yield mitochondria which are sensitive to inhibition by rotenone when respiring NAD⁺-Minked substrates and have 3 sites of phosphorylation. The levels of cytochromes (a + a ₃), b , and c are similar in mitochondria isolated from log or stationary phase amebae, and, with the exception of succinate, the respiratory rates obtained with different substrates do not change significantly from log to stationary growth phase.