An atypical cytochrome b in the colorless alga Polytomella spp.: The high potential b(H) heme exhibits a double transition in the a-peak of its absorption spectrum
Por:
Gutiérrez-Cirlos E.-B., Gómez-Lojero C., Vázquez-Acevedo M., Pérez-Martínez X., González-Halphen D.
Publicada:
1 ene 1998
Resumen:
Polytomella spp. is a colorless alga of the family Chlamydomonadaceae that lacks chloroplasts and cell wall. A highly active ubiquinol-cytochrome c oxidoreductase (bc1 complex), sensitive to antimycin and myxothiazol, has been purified and characterized from this alga (Gutierrez-Cirlos et al., 1994, J. Biol. Chem. 269, 9147-9154). Both in mitochondrial membranes and in the isolated complex, the visible spectrum of cytochrome b from Polytomella spp. exhibits an atypical ?-band with a maximum at 567 nm. This maximum is shifted 3-4 nm to the red when compared with b-type cytochromes from other organisms. Analysis of the b hemes of the bc1 complex by high performance liquid chromatography revealed no differences in the retention time and in the absorption spectra of the b-type hemes from Polytomella spp. and hemin, indicating that the prosthetic group in this alga is protoheme and thus ruling out the possibility that the red-shift could be due to different chemical substitutions in the porphyrin rings of the b(L) or b(H) hemes. The two b hemes were characterized by electrochemical redox titration; at pH 7.8- 8.0, the midpoint potential for b(L) was -143 mV and for b(H) +25 mV. The spectra of the two b-type hemes were recorded in the presence of different reductants, at selected electrochemical potentials, and in the presence of antimycin A, to distinguish between the contribution of b(L) and b(H) to the visible spectrum. Both hemes b(L) and b(H) of the algal cytochrome b contribute to the observed bathochromic absorption maximum in the ?-band of the spectrum. The data also show that the low potential b(L) heme from Polytomella spp. is spectroscopically similar to that of other organisms, with two transitions in the ?-peak at 558.7 and 568.4 nm. The high- potential heme b(H) also exhibits a spectrum with two transitions at 557.2 and 568.9 nm, which surprisingly differs from the spectra of cytochrome b(H) of mammals, plants, yeasts, and bacteria, which all exhibit a single transition centered around 560 nm.
Filiaciones:
Gutiérrez-Cirlos E.-B.:
Depto. de Genética Molecular, Inst. de Fisiología Celular, Univ. Nac. Auton. de México, Apartado Postal 70-243, Mexico City, DF 04510, Mexico
Gómez-Lojero C.:
Departamento de Bioquímica, CINVESTAV del IPN, Mexico City, Mexico
Vázquez-Acevedo M.:
Depto. de Genética Molecular, Inst. de Fisiología Celular, Univ. Nac. Auton. de México, Apartado Postal 70-243, Mexico City, DF 04510, Mexico
Pérez-Martínez X.:
Depto. de Genética Molecular, Inst. de Fisiología Celular, Univ. Nac. Auton. de México, Apartado Postal 70-243, Mexico City, DF 04510, Mexico
González-Halphen D.:
Depto. de Genética Molecular, Inst. de Fisiología Celular, Univ. Nac. Auton. de México, Apartado Postal 70-243, Mexico City, DF 04510, Mexico
|