Purification of a Ca2+/Calmodulin-dependent Protein Kinase from Baker's Yeast

Summary: A Ca2+- and calmodulin-dependent protein kinase was purified from baker's yeast to near homogeneity. At pH 7·5 and 0·1 M-NaCl it has a native molecular mass close to 100 kDa, and is a dimer of apparently identical 56 kDa autophosphorylatable subunits. At 60 μM-CaCl2 and with mixed histones as substrate, half-maximal activation required concentrations of beef calmodulin above 1 μM. At 0·14uM-beef calmodulin the enzyme showed apparent negative cooperativity towards ATP, with limiting apparent K m values of 4 μM and 60 μM ATP. The enzyme has a broad substrate specificity in vitro, including two yeast proteins that yield, respectively, 50 kDa and 200 kDa phosphopolypeptides.