The Effect of Inhibitors on the Oxygen Kinetics of Terminal Oxidases of Tetrahymena pyriformis ST

Abstract

Respiration of early-exponential phase cultures of the ciliate protozoon Tetrahymena pyriformis is inhibited in two stages with increasing concentrations of cyanide. Up to 40 to 50 % inhibition occurs at low concentrations (< 15 PM). Maximal inhibition was obtained with 300pwcyanide; at this concentration 20 % of the respiration was still unaffected.Competitive inhibition of respiration by CO occurs (Ki = 4-25 p~) ; azide inhibition of oxygen consumption is uncompetitive (K, = 4 to 9 mM). A salicylhydroxamic acid-sensitive oxidase is present which is not inhibited by cyanide, azide, CO or H,S. Three other pathways of terminal oxidation are present which are insensitive to azide, CO and salicylhydroxamic acid. One of these is cyanide-and sulphide-sensitive, a second is cyanide-insensitive but sulphide-sensitive, and a third is cyanide-sensitive but sulphide-insensitive ; these pathways may not possess unique terminal oxidases. No oxidase with a very low affinity for oxygen was detected, but the overall affinity for oxygen of T. pyriformis in the absence of inhibitors (K, = 2.9 PM) is lower than that of some other protozoa.

The SHAM-sensitive Alternative Oxidase in Tetrahymena pyriformis: Activity as a Function of Growth State and Chloramphenicol Treatment

“…The results with respect to general levels of respiration and inhibitor sensitivity for exponentially growing and stationary phase cells are in good agreement with previously published data (Ruben & Hooper, 1978;Lloyd et al, 1980;Skriver & Nilsson, 1978).…”

“…At higher concentrations, the degree of inhibition attainable (approximately 50 % at 4 to 5 mM) suggests a non-specific effect presumably due to the chelating properties of the inhibitor. Lloyd et al (1980) found no effect of SHAM at 1 mM in whole cells in the absence of CN-; however, their cultures were at high density (4 x lo5 cells rnl-l, concentrated to 2 x lo6 cells ml-l for measurement) and therefore appear to be more typical of the stationary phase cells used here. Data on the absolute level of O2 consumption per cell were not presented by these authors so that the physiological growth state can not be assessed.…”

“…In fungi, however, it is known that growth in the presence of inhibitors of mitochondrial translation results in an enhancement and greater utilization of the salicylhydroxamic acid (SHAM)-sensitive alternative oxidase (Hanssens & Verachtert, 1976;Vanderleyden et al, 1979;Lambowitz et al, 1972a, b ;reviewed in Henry & Nyns, 1975). Since Tetrahymena has an alternative oxidase (Eichel & Stearns, 1977;Stearns et al, 1978;Lloyd et al, 1980), it seemed likely that following CAP-treatment this pathway would become more active. Under these conditions, since both sites I1 and I11 of oxidative phosphorylation were not utilized (Henry & Nyns, 1975), there would be less ATP production for a given level of O2 consumption and, although the level of O2 consumption was similar, this would make for a major distinction between the energetics of the stationary phase and of the CAP-treated cell.…”

Oxygen Affinities of the Hydrogenosome-containing Protozoa Tritrichomonas foetus and Dasytricha ruminantium, and Two Aerobic Protozoa, Determined by Bacterial Bioluminescence

“…min-I. Gas entry and exit ports were via the lid (Degn et al, 1980). The vessel was jacketed and supplied with water from a thermostatically controlled water heater.…”

Mitochondrial Sulfide Oxidation in Arenicola Marina

“…Maximal inhibition of respiration, thcrefore, could only be obtained in the presence of the classical inhibitors plus salicylhydroxamic acid (Lloyd et al, 1979(Lloyd et al, , 1980Mendis and Evans, 1984;Paget et al, 1987b;Zaba, 1983). The alternative pathway of A. marina seeins to differ from that of most other species since it is not completely insensitive to cyanide.…”