| Abstract: | Whole cell respiration rates were measured polarographically for Naegleria gruberi during growth in agitated cultures. Log growth phase amebae consumed 80 ng atoms O/min/mg cell protein. At stationary phase, respiration rate decreased 4–fold. Intact mitochondria were isolated from N. gruberi and their oxidative and phosphorylative capacities were studied polarographically. As with the mammalian system, the mitochondria oxidized succinate and NAD-linked substrates, but unlike rat liver mitochondria, those from the protozoan rapidly oxidized citrate and NADH. The rates of substrate oxidation were ADP-dependent, with ADP:O ratios equalling ? 2.8 for NAD-linked substrates and ? 2.2 for succinate. The respiratory control ratios. 2 to 4 for 11 substrates, were dependent on Pi, Mg2+, and serum albumin. Potassium cyanide, azide, malonale, and rotenone inhibited electron transport the same way as that of the mammalian system: however, amytal inhibited both glutamate and succinate respiration. Pentachlorophenol, DNP, and bilirubin uncoupled oxidation from phosphorylation. Difference spectra of oxidized and dithionite-reduced mitochondria had distinct absorption bands of flavins and of c-, b-, and α-type cytochromes. |
