Mitochondrial creatine kinase with atypical pI values detected in serum of a patient with ovarian hepatoid yolk sac tumor

Atypical mitochondrial creatine kinase (creatine N-phosphotransferase, CK, EC 2.7.3.2) was detected in the serum of a patient with carcinoma of germ cell origin, probably hepatoid yolk sac tumor. The pI of the oligomeric atypical mitochondrial CK (Mi-CK) was found at the acidic side compared to that of the typical ubiquitous Mi-CK (uMi-CK), while the molecular size of the atypical Mi-CK was similar to that of the typical uMi-CK. The pIs of the oligomeric and the dimeric atypical Mi-CKs became the same as those of the typical uMi-CK upon treatment with 2-mercaptoethanol. Therefore, the atypical Mi-CK was suggested to be an oxidized form of uMi-CK, and the oxidation might have occurred in the mitochondria because the oligomeric atypical Mi-CK had atypical pIs. The physicochemical characteristics of the oxidized uMi-CK were similar to those of the typical uMi-CK.