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 (k(on)) is 6.8 × 10(4)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); k(on)=3.2 × 10(5)M(-1)s(-1)). Moreover, CL binding to CM-cytc-Fe(III) facilitates peroxynitrite isomerization (k(on)=5.3 × 10(5)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.