ELONGATION FACTOR-II KINASE - IMMUNOLOGICAL EVIDENCE FOR THE EXISTENCE OF TISSUE-SPECIFIC ISOFORMS

eEF-2 kinase is a ubiquitous Ca2(+)/calmodulin-dependent protein kinas e that is specific for protein synthesis elongation factor-2 (eEF-2). This study describes an improved procedure for the purification of eEF -2 kinase from rabbit reticulocyte lysate. The eEF-2 kinase preparatio n was used to raise polyclonal antibodies, which immunoprecipitated eE F-2 kinase protein and activity from rabbit reticulocyte lysate. The a ntibodies recognized a single 103 kDa band in extracts from several ce ll lines including NIH 3T3, PC12, C6 glioma, HeLa, and MCF-7 breast ca rcinoma. However, there was no immunoreactivity in extracts of rabbit or bovine liver or rabbit kidney despite the presence of abundant eEF- 2 kinase activity in these tissues. Exposure of PC12 cells to nerve gr owth factor (NGF) resulted in rapid down-regulation of eEF-2 kinase ac tivity and a decrease in immunoreactivity. After 24 h of incubation wi th NGF, the activity of the kinase recovered to 80% of initial values. In contrast, the immunoreactivity of eEF-2 kinase continued to decrea se. These data suggest that tissue-specific isoforms of eEF-2 kinase m ay exist and that these isoforms may be regulated by growth factors.