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

1. Purified mitochondria have been prepared from wild type Paramecium tetraurelia and from the mutant Cl1 which lacks cytochrome aa3. Both mitochondrial preparations are characterized by cyanide insensitivity. Their spectral properties and their redox potentials have been studied. 2. Difference spectra (dithionite reduced minus oxidized) of mitochondria from wild type P. tetraurelia at 77 K revealed the alpha peaks of b-type cytochrome (s) at 553 and 557 nm, of c-type cytochrome at 549 nm and a-type cytochrome at 608 nm. Two alpha peaks at 549 and 545 nm could be distinguished in the isolated cytochrome c at 77 K. After cytochrome c extraction from wild type mitochondria, a new peak at 551 nm was unmasked, probably belonging to cytochdrome c1. The a-type cytochrome was characterized by a split Soret band with maxima at 441 and 450 nm. The mitochondria of the mutant Cl1 in exponential phase of growth differed from the wild type mitochondria in that cytochrome aa3 was absent while twice the quantity of cytochrome b was present. In stationary phase, mitochondria of the mutant were characterized by a new absorption peak at 590 nm. 3. Cytochrome aa3 was present at a concentration of 0.3 nmol/mg protein in wild type mitochondria and ubiquinone at a concentration of 8 nmol/mg protein both in mitochondria of the wild type and the mutant Cl1. Cytochrome aa3 was more susceptible to heat than cytochromes b and c,c1.