Peroxynitrite detoxification by horse heart carboxymethylated cytochrome c is allosterically modulated by cardiolipin

Carboxymethylation of equine heart cytochrome c (cytc) changes its tertiary structure by disrupting the heme-Fe-Met80 distal bond, such that carboxymethylated cytc (CM-cytc) displays myoglobin-like properties. Here, the effect of cardiolipin (CL) on peroxynitrite isomerization by ferric CM-cytc (CM-cytc-Fe(III)) is reported. Unlike native ferric cytc (cytc-Fe(III)), CM-cytc-Fe(III) catalyzes peroxynitrite isomerization, the value of the second order rate constant (kon) is 6.8 × 104 M−1 s−1. However, CM-cytc-Fe(III) is less effective in peroxynitrite isomerization than CL-bound cytc-Fe(III) (CL-cytc-Fe(III); kon = 3.2 × 105 M−1 s−1). Moreover, CL binding to CM-cytc-Fe(III) facilitates peroxynitrite isomerization (kon = 5.3 × 105 M−1 s−1). Furthermore, the value of the dissociation equilibrium constant for CL binding to CM-cytc-Fe(III) (K = 1.8 × 10−5 M) is lower than that reported for CL-cytc-Fe(III) complex formation (K = 5.1 × 10−5 M). Although CM-cytc-Fe(III) and CL-cytc-Fe(III) display a different heme distal geometry and heme-Fe(III) reactivity, the heme pocket and the CL cleft are allosterically linked.

► Peroxynitrite isomerization by carboxymethylated cytochrome c.
► Cardiolipin-dependent peroxynitrite isomerization by carboxymethylated cytochrome c.
► Cardiolipin binding to carboxymethylated cytochrome c.
► Pro-apoptotic effects of the cardiolipin–cytochrome c complex.
► Anti-apoptotic effects of the cardiolipin–cytochrome c complex.