Quantification of tumor type M2 pyruvate kinase (Tu M2-PK) in human carcinomas

Proliferating and tumor cells express a certain isoenzyme of pyruvate kinase, called PK type M2. This isoenzyme can be isolated in an active tetrameric and an inactive dimeric form. We have termed this form tumor type M2-PK. This tumor type pyruvate kinase can be quantified by a specific ELISA in blood sera and tumor homogenates. In this study we have compared 26 normal colon mucosa and colon cancer specimens from the same patients. The total specific pyruvate kinase activity and the amount of the tumour type M2-PK measured by ELISA was increased in the tumor samples compared to the normal colon mucosa of the same patient. In normal colon mucosa the specific PK-activity ranged between 0.21 and 1.25 U/mg protein whereas in colon carcinoma we found activities between 0.99 and 7.08 U/mg. The amount of tumor M2-PK measured by ELISA ranged between 0.82 and 27.10 U/mg protein in normal colon mucosa and between 1.96 and 242.40 U/mg protein in colon carcinoma. The tumor M2-PK content in the serum of 666 healthy blood donors was measured by ELISA and compared to sera from 15 colon carcinoma patients and showed a highly significant difference (Mann-Whitney rank sum test, p < 0.001). The values for the 50%-percentiles (median) of blood donors were 10.8 U/ml and 55.0 U/ml for colon carcinoma.