CYTOCHROME C-553 FROM 2 SPECIES OF MACROALGAE

Cytochrome c-553 has been purified to homogeneity from the red macroalgae Chondrus crispus and Porphyra umbilicalis. Whereas Porphyra a umbilicalis possessed a single cytochrome c-553, isoforms of the cytochrome in approximate ratio 4:1 were found in Chondrus crispus. The M(r) of all the cytochromes was 12 000 as measured by SDS-PAGE. The absorption spectrum of the reduced cytochromes showed maxima at 270-272 nm (protein), 414-416 nm (gamma-peak), 522 nm (beta-peak) and 553 nm (alpha-peak) and molar extinction coefficients were consistent with a single haem per molecule. The gamma to alpha absorption ratio was close to 7.0 for the Porphyra umbilicalis cytochrome and Chondrus crispus major cytochrome. Reduce-oxidised difference spectra were closely similar. The midpoint redox potentials of the one-electron transfers were + 340 mV for the Porphyra umbilicalis cytochrome c-553, and + 330 and + 285 mV for the major and minor isoforms from Chondrus crispus. While the cytochromes of highest redox potential are presumed to be implicated in photosynthetic electron transport in place of plastocyanin, which these algae apparently lack, the metabolic role for the Chondrus crispus minor cytochrome c-553 is enigmatic.