Quantitative detection of tumor M2-PK in serum and plasma

The majority of turners express an isoform of the glycolytic enzyme pyruvat e kinase, the type tumor M2. The isoenzyme exists in an active tetrameric a nd a less active dimeric form. The dimeric form is strongly overexpressed i n tumor cells and this new tumor marker is thus called tumor M2-PK. This is oenzyme is released from tumor cells and is quantitatively detectable in bo dy fluids by a sensitive enzyme-linked immunosorbent assay (ELISA). To esta blish the ELISA for the routine diagnostic in a clinical laboratory, the sa mple stability was evaluated. Therefore, blood samples were collected in di fferent ways from healthy donors. Reproducibility of tumor M2-PK detection in EDTA-plasma was not affected by the day to day 'stress' in a clinical ro utine (e.g. shaking, leaving the samples at room temperature for several ho urs without prior centrifugation). Similar results were obtained with citra te-plasma, whereas detection in serum and heparin-plasma was only reproduci ble when the blood samples were centrifuged within 2 hrs after collection. It appears that lymphocytes contain small amounts of the tumor M2-PK isoenz yme. They might release tumor M2-PK in heparin-plasma and serum samples, bu t not in EDTA-plasma samples. The results indicated that EDTA-plasma appear s to be most appropriate for the routine diagnostic of tumor M2-PK as a tum or marker.