A sandwich ELISA for phosphoglycerate kinase.

Phosphoglycerate kinase (PGK1) is a key enzyme in glycolysis that can also be released from certain cells. In the extracellular milieu, PGK1 reportedly acts as a disulphide reductase to activate plasmin, resulting in the production of angiostatin, a potent angiogenesis inhibitor. Certain cancer cell lines secrete unusually large amounts of PGK1, raising the possibility that serum PGK1 levels can be used to screen for cancer. To facilitate the characterization of the PGK1 secretory pathway and to monitor serum levels of PGK1, we have developed a sensitive sandwich ELISA using an immuno-affinity-purified chicken polyclonal antibody for capturing PGK1 and an immuno-affinity-purified rabbit polyclonal antibody for detecting it. The assay is about 10-fold more sensitive than other reported PGK1 ELISAs. We used the ELISA to quantify the amount of PGK1 released from HeLa cells and PGK1 serum levels in cancer patients. Of 10 cancer patients whose serum was tested, 3 of 4 with pancreatic cancer had 65-900% higher levels of PGK1 than that found in normal serum.