Kinetic and equilibrium studies of alkaline isomerization of vertebrate cytochromes c

https://doi.org/10.1016/0005-2795(81)90217-8Get rights and content

Abstract

Equilibria and kinetics of alkaline isomerization of seven ferricytochromes c from vertebrates were studied by pH-titration and pH-jump methods in the pH region of 7–12. In the equilibrium behavior, no significant difference was detected among the cytochromes c, whereas marked differences in the kinetic behavior were observed. According to the kinetic behavior of the isomerization, the cytochromes c examined fall into three classes: Group I (horse, sheep, dog and pigeon cytochromes c), Group II (tuna and bonito cytochromes c) and Group III (rhesus monkey cytochrome c). The kinetic results are interpreted in terms of the sequential scheme:

where the neutral and alkaline forms are the species stable at neutral and alkaline pH, respectively, and the transient form is a kinetic intermediate. From comparison of the primary sequences of the seven cytochromes c and the classification of these cytochromes c, it is concluded that the amino acid substitution Phe/Tyr at the 46-th position has a major influence on the kinetic behavior. In Group II and III cytochromes c, the ionization of Tyr-46 is suggested to bring about loosening of the heme crevice and thus facilitate the ligand replacement involved in the isomerization.

References (34)

  • R.E. Dickerson et al.

    J. Biol. Chem.

    (1971)
  • R. Swanson et al.

    J. Biol. Chem.

    (1977)
  • D.O. Lambeth et al.

    J. Biol. Chem.

    (1973)
  • D.L. Brautigan et al.

    J. Biol. Chem.

    (1977)
  • R.K. Gupta et al.

    Biochem. Biophys. Res. Commun.

    (1971)
  • I. Morishima et al.

    Biochim. Biophys. Acta

    (1977)
  • A. Schejter et al.

    J. Biol. Chem.

    (1978)
  • L.A. Davis et al.

    J. Am. Chem. Soc.

    (1974)
  • G. Czerlinski et al.

    Arch. Biochem. Biophys.

    (1971)
  • H. Kihara et al.

    Biochim. Biophys. Acta

    (1976)
  • T. Yamanaka et al.

    Biochim. Biophys. Acta

    (1964)
  • E. Margoliash et al.

    Methods Enzymol.

    (1967)
  • A. Schejter et al.

    Biochim. Biophys. Acta

    (1963)
  • R.E. Dickerson et al.
  • T. Takano et al.

    J. Biol. Chem.

    (1977)
  • R.E. Dickerson et al.
  • N. Osheroff et al.

    J. Biol. Chem.

    (1980)
  • Cited by (16)

    • Humanlike substitutions to Ω-loop D of yeast iso-1-cytochrome c only modestly affect dynamics and peroxidase activity

      2018, Journal of Inorganic Biochemistry
      Citation Excerpt :

      It also grew in abruptly above pH 9.5 with an apparent pKa of 10.75 and n ~ 4. High pH fast phases on the 10–50 ms time scale for the alkaline transition have been reported previously for mammalian cytochromes c [49–53]. These phases have been attributed to unfolding of the least stable substructure of Cytc [49], formation of a weakened heme-Met80 bond [51,52] or displacement of Met80 by hydroxide [51].

    View all citing articles on Scopus
    View full text