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The origin of an atypical creatine kinase (CK, ATP:creatine N-phosphotransferase, EC 2.7,3.2) migrating cathodic to the MM position found in the serum of a cancer patient was studied. The electrophoretic mobility of the atypical CK is similar to that of the fast-moving cathodal mitochondrial CK. The relative molecular mass was estimated to be approximately 350000, and was similar to that of the fast-moving cathodal mitochondrial CK. The atypical CK reacted with anti-human mitochondrial CK antibody. It is therefore suggested that the atypical CK is of mitochondrial origin. After incubation in 2 mol/l urea, the enzyme was converted into a new form migrating to the MM position. The conversion was observed in liver mitochondrial CK but not heart mitochondrial CK. The residual CK activity after heating at 56 degrees C for 60 s was 77%, and the apparent Km value for creatine phosphate at 30 degrees C was about 0.27 mmol for the atypical CK. These characteristics were very similar to those of the liver mitochondrial CK, because the data from the enzyme determined at the same time were 75% for residual enzyme activity to heat, and 0.24 mmol for apparent Km value. Therefore liver mitochondria are suggested to be the source of the atypical CK.

Mitochondrial creatine kinases (CKs, ATP:creatine N-phosphotransferases, EC 2.7.3.2) were isolated from normal human heart and liver, and their characteristics were compared. The electrophoretic patterns of the extracted enzymes exhibited two forms both migrating cathodic to CK-MM. The fast-moving cathodal form is the major form and the slow-moving cathodal form is the minor one. Incubation of the heart mitochondrial CK at 37 degrees C in normal human serum for 7 h and of the liver mitochondrial CK at 26 degrees C for 1 h in 2 mol/l urea, converted the fast-moving form into the slow-moving one, and finally into a third form migrating in the MM position. The relative molecular masses were estimated to be approximately 350,000 for the major form, and 80,000 for the minor and the third forms. The electrophoretic mobility and molecular weight of the third form were identical to those of the CK-MM; however, the third form was distinguished from CK-MM by its different antigenicity. Thus, three forms were ultimately recognized as mitochondrial CKs by electrophoretic mobilities and molecular weights. The liver mitochondrial CK reacted with anti-human heart mitochondrial CK antibody, thus these two isoenzymes could not be discriminated by their antigenicities. The liver mitochondrial CK was more stable to heat and had higher apparent affinity for creatine phosphate than the heart mitochondrial CK.

A new creatine kinase (CK, ATP: creatine N-phosphotransferase, EC 2.7.3.2) band was found in mitochondrial extracts prepared from malignant liver tissue. By agar gel electrophoresis the new band (CKmLT) migrated between CK-MM and a sample application point. The CK band was not found in mitochondrial extracts of normal liver, cytosolic extracts of normal and malignant liver homogenates. We thus presume that the origin of CKmLT is from mitochondria of malignant liver tumors. CKmLT reacted with anti-mitochondrial CK antibodies so that its antigenicity was similar to that of mitochondrial CK. Physico-chemical characteristics were similar to those of the polymeric form of the normal liver mitochondrial CK (CKmL1); i.e. relative molecular mass (320 000 to 350 000), heat stability, and the behavior in 2 mol/l urea. CKmLT migrated to the CKmL1 and the MM position after long-term storage at -20 degrees C. CKmLT did not demonstrate affinity to concanavalin A, and there was no significant change in the electrophoretic mobility of CKmLT following neuraminidase treatment.

Sera from 167 patients with malignant tumor were examined with regard to mitochondrial creatine kinase (ATP: creatine N-phosphotransferase, EC 2.7.3.2, CK). The CK (CKm) was detected in 66 cases (40%), in 42 of 96 men and in 24 of 71 women. Seventeen patients had hepatic carcinomas and 14 gastric carcinoma. CKm was also present in sera from patients with malignancy of the lung, the mammary gland etc. In the CKm positive group, about 85% had metastatic and/or infiltrating malignancy, and about 90% were undergoing chemotherapy. The figures resembled those in the CKm negative group. Mortality rates in the CKm positive group were 1.7 times higher than in the CKm negative group. CKm may be a marker of some biological factors leading to and/or resulting from a poor prognosis and not simply of primary or metastatic tumors. Most of the total serum CK activities in the CKm positive group were within normal limits. CKm activities in the gastric carcinoma group were higher than those in other groups, particularly in comparison to the liver carcinoma group.

Three electrophoretically atypical creatine kinase (CK) bands were found simultaneously in the serum of a patient with terminal carcinoma of the colon. The atypical CKs were found at the cathodal side of CK-MB (CK-X1), at a sample application point (CK-X2), and at the anodal side of CK-MM (CK-X3) on agar plates. Our data seemed to suggest that CK-X1 was predominantly a CK-IgA/beta-lipoprotein complex, CK-X3 was a CK-IgG complex, and CK-X2 was macromolecular, different from both CK-X1 and CK-X3. The light chains of IgA and IgG were both of the lambda type. All native isoenzymes comprising these atypical CKs were identified as MM type. There was no change of the electrophoretic pattern of serum CK isoenzymes throughout the course of the study.