Phospholipid‐sensitive Ca2+‐dependent protein kinase phosphorylates the β subunit of eukaryotic initiation factor 2 (eIF‐2)

Abstract The ability of homogeneous phospholipid-sensitive Ca 2+ -dependent protein kinase (PL-Ca-PK) from pig spleen to phosphorylate eukaryotic initiation factor 2 (eIF-2) was examined. PL-Ca-PK phosphorylated the β-subunit of eIF-2, whereas myosin light chain kinase (MLCK) and cyclic AMP- and cyclic GMP-dependent protein kinases (cA-PK and cG-PK) did not. PL-Ca-PK could incorporate a maximum of 1.6 mol phosphate/mol eIF-2. The app. K m and V max for PL-Ca-PK phosphorylation of eIF-2 were 0.13 μM and 0.02 μmol. min −1 .mg enzyme −1 , respectively. Phosphoamino acid analysis revealed that incorporation of phosphate into eIF-2 occurred almost exclusively at serine residues. These findings indicate that eIF-2 was an effective substrate for PL-Ca-PK, suggesting that this enzyme may play a role in the regulation of protein synthesis.