New isoforms of cytochrome c oxidase subunit IV in tuna fish.

In the present study, the cDNA sequences of cytochrome c oxidase subunit IV isoforms from tuna fish are reported. The cDNAs share 57% identity among each other and the deduced amino acid sequences of the mature proteins 56% identity. Until now, only in yeast are two isoforms of the corresponding subunit V known, which are expressed in response to the oxygen supply. The hypothetical function of the new isoforms in fish for adaptation to different oxygen partial pressures in tissues of higher organisms is discussed.