Optical and Potentiometric Study of the b- and c-Type Cytochromes in Mushroom Agaricus bisporus Lge Mitochondria.

Differential spectrometry revealed two species for the b-type, as well as for the c-type, cytochromes in mitochondria from Agaricus bisporus Lge. The two b-type components are denoted according to their peak position in the alpha region at room temperature, i.e. b(560) and b(566). The b(556) component present in all the studied higher plant mitochondria was not detected in the system. At 293 K, the c-type cytochromes exhibit a common alpha band with a maximum at 550 nanometers. This band is split at 77 K, with peak positions at 547 nanometers (cytochrome c) and 552 nanometers (cytochrome c(1)).Redox titrations, analyzed according to a new method (Denis, Neau, Blein 1980 Bioelectrochem Bioenerg 7: 757-773), also yielded the resolution of two species of b-type and c-type cytochromes. The b components have midpoint potential values at pH 7.2 and 20 C of E(m1) = 40 +/- 10 millivolts and E(m2) = 175 +/- 10 millivolts. Their calculated individual difference spectra exhibit alpha bands with identical maxima at 561 nanometers, in contrast with optical observations. The midpoint potential values of the resolved c components are 210 +/- 10 millivolts and 292 +/- 5 millivolts at pH 7.2 and 20 C. Their corresponding calculated difference spectra have their alpha band maxima at 553 and 551 nanometers. These two species have been identified respectively with cytochrome c(1) and cytochrome c. The ratio of the maximum optical contributions, c/c(1), is in the range 4/1 to 5/1, in contrast with other results related to yeast or higher plant mitochondria where it amounts to 2/1 or even 1.3/1.