Although it is known that neutrophils infiltrate damaged sites immediately after tissue injury, the
endogenous factors that induce their acute transmigration and activation have not been thoroughly investigated.
For the candidates of those factors, we recently discovered two novel neutrophil-activating cryptides,
mitocryptide-1 (MCT-1) and mitocryptide-2 (MCT-2), hidden in mitochondrial proteins. In addition, many
unknown neutrophil-activating peptides other than MCT-1 and MCT-2 were also observed during their purification.
Here, we isolated and purified a novel neutrophil-activating peptide from porcine hearts, which
we showed by structural analyses to have an identical primary structure to porcine mitochondrial cytochrome
c (68-85). We named this novel functional octadecapeptide as mitocryptide-CYC (MCT-CYC).
Structure-activity relationships of cytochrome c on β-hexosaminidase (β-HA) release from neutrophilic-differentiated HL-
60 cells demonstrated that peptides derived from the C-terminal part of cytochrome c induced β-HA release and that cytochrome
c (70-85) was the most potent cryptide among them. Since cytochrome c is known to be involved in the apoptotic
process, our results suggest that cryptides, including MCT-CYC, derived from mitochondrial cytochrome c are possible
factors that induce scavenging of toxic debris produced from apoptotic cells by neutrophils.
Keywords: Cryptide, cytochrome c, mitochondria, mitocryptide-1, mitocryptide-2, mitocryptide-CYC, neutrophil, arboxypeptidases, neutrophil-activating peptide, Peptidergic neurotransmitters
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