The respiratory chain of Paramecium tetraurelia in wild type and the mutant Cl1. I. Spectral properties and redox potentials

Isolation of the membranes from secretory organelles (trichocysts) of Paramecium tetraurelia

We present for the first time a method for isolation of the membranes of extrusive organelles (trichocysts) from sterile culture of different strains of Paramecium tetraurelia. First, trichocysts are isolated according to a new method (Glas-Albrecht, R. and Plattner, H. (1990) Eur. J. Cell Biol. 53, 164-172) with high purity and yield. Then the organelles are subjected to osmotic swelling. Since trichocysts then easily 'decondense' and entangle membranes, these cannot be isolated directly by centrifugation, but only by passage through a filter and subsequent centrifugation. Purity of membrane fractions is analysed by electron microscopy and SDS-PAGE, combined with silver staining or, after biotinylation, by avidin-peroxidase labelling. Molecular masses resolved in our gels are in a range from less than or equal to 15 to greater than or equal to 105 kDa. Main bands obtained with nd9-28 degrees C trichocyst membranes (most bands also being common to wild type trichocysts) are of about 16.5, 19-21, 27-29, 33-34, 44-45 (strong), 47-48 (strong), 57, 61, 65 (strong), 68-71, 75, 81, 94-95 (strong), 104 and greater than or equal to 110 kDa, from a total of approx. 23 bands resolved. There is no remarkable occurrence of dominant protein bands from trichocyst contents ('trichynins'), though these might represent up to 10(3)-times more of the total trichocyst proteins. The ratio of phospholipid/protein is approx. 0.2 mg/mg. The methodology developed might also be valuable for the isolation of extrusome membranes from some other protozoan species.

AMP-dependence of the cyanide-insensitive pathway in the respiratory chain of Paramecium tetraurelia

The AMP-dependent stimulation of the cyanide-insensitive respiration of Paramecium mitochondria was investigated. The nucleotides exhibiting a stimulatory effect on the cyanide-insensitive oxidation of pyruvate (+ malate) in a medium supplemented with EDTA or carboxyatractyloside were, in decreasing order of efficiency, AMP, GMP, IMP, UMP and TMP. On the other hand, ADP, ATP and cyclic AMP were ineffective. In the presence of carboxyatractyloside, addition of AMP to Paramecium mitochondria incubated with pyruvate (+malate) led to an increase in membrane potential. In the absence of light, the photoactivable derivative of AMP, 3'-[4-[N-(4-azido-2-nitrophenyl)amino]butyryl]-AMP (NAP4-AMP) added to Paramecium mitochondria opposed the stimulatory effect of AMP on the cyanide-insensitive respiration; the Ki for NAP4-AMP was much lower than the Km for AMP, 0.2 microM compared with 120 microM. The ADP-stimulated respiration was not affected. Photoirradiation of Paramecium mitochondria in the presence of NAP4-AMP resulted in irreversible inhibition of the AMP-stimulated cyanide-insensitive respiration. No effect on the ADP-stimulated respiration was observed. A heatlabile cyanide-insensitive ubiquinol oxidase was extracted from Paramecium mitochondria with the detergent NN-dimethyl-N-(3-laurylamidopropyl)amine oxide. The quinol oxidase activity was slightly stimulated by AMP.

Genetic interactions in the control of mitochondrial functions in Paramecium. I. Interactions between nuclear genes

The genetic and physiological properties of two nuclear mutants of Paramecium tetraurelia affecting mitochondrial properties, and first screened as resistant to tetrazolium (TTC) are described. The mutant TTC64-1R is strongly deficient in cytochrome c and the mutant TTC66pR is partially deficient in cytochrome aa3; both mutants display cyanide insensitive respiration in exponential growth phase. In the double mutant TTC64-1R -- TTC66pR/TTC64-1R -- TTC66pR the deficiency in cytochrome aa3 due to the TTC66pR mutation is suppressed. The mutation TTC64-1R does not suppress cytochrome aa3 deficiencies due to mitochondrial mutations, but does interact with another nuclear mutation, cl1, (compatible only with mitochondria deficient in cytochrome oxidase) in such a way that the double mutant TTC64-1R -- cl1/TTC64-1R -- cl1 displays a normal amount of cytochrome aa3. The possible mechanisms and physiological significance of these suppressive effects are discussed.

The respiratory chain of Paramecium tetraurelia in wild type and the mutant Cl1. II. Cyanide-insensitive respiration. Function and regulation

1. The cyanide-insensitive respiration in Paramecium tetraurelia was found to be located in mitochondria. 2. Sensitivity of the mitochondrial respiration to cyanide depended on growth conditions. Under standard conditions of growth, 15--20% of respiration was insensitive to 1 mM cyanide. Full resistance to 1 mM cyanide was observed by growing cells in the presence of erythromycin (100--400 microgram/ml) 0.2 mM cyanide. The mitochondrial respiration of the mutant Cl1 harvested during the exponential phase of growth was largely insensitive to cyanide (more than 80%). 3. Pyruvate was oxidized at the same rate by wild type mitochondria and mitochondria of the mutant Cl1. In contrast, succinate oxidation was 2--3 times faster in mitochondria of the mutant Cl1 than in wild type mitochondria. 4. The cyanide-insensitive respiration was inhibited by 1 mM salicylhydroxamic acid to nearly 100%. Other efficient respiratory inhibitors included amytal and heptylhydroxyquinoline. Antimycin was not inhibitory even at concentrations as high as 5 microgram/mg protein, a finding consistent with the lack of antimycin binding sites.