Purification and properties of a ribosomal casein kinase from rabbit reticulocytes.
A casein kinase was isolated and purifed from rabbit reticulocytes. About 90% of the enzyme activity co-sedimented with the ribosomal fraction, whereas about 10% of the enzyme activity was found in the ribosome-free supernatant. Both casein kinases (the ribosome-bound enzyme as well as the free enzyme) showed identical activity and the same molecular weight. On sodium dodecyl sulphate/polyacrylamide-gel electrophoresis a single band of about 70 000 mol.wt. was observed. Sucrose-gradient analysis, however, showed that the enzyme activity sedimented with a s20,w of approx. 7.5S. This observation suggested that the casein kinase is a dimer composed of subunits of identical molecular weight. The enzyme utilizes GTP as well as ATP as a phosphoryl donor. It preferentially phosphorylates acidic proteins, in particular the model substrates casein and phosvitin. Casein kinase is cyclic AMP-indepenoent. The Km values for ATP and GTP with phosvitin as a substrate were determined as 1.2 and 8.8 micrometer respectively.
D000818:Animals; D002364:Caseins; D002499:Centrifugation, Density Gradient; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008970:Molecular Weight; D009711:Nucleotides; D011494:Protein Kinases / Q000302:isolation & purification*; D011817:Rabbits; D012156:Reticulocytes / Q000201:enzymology*; D012270:Ribosomes / Q000201:enzymology*; D013379:Substrate Specificity
D002364:Caseins; D009711:Nucleotides; D011494:Protein Kinases