Specificity of a phosphatase for phospholipid, Ca²⁺-dependent protein kinase-phosphorylated histone H1 resides in the catalytic subunit

A protein phosphatase from liver which acts preferentially on histone phosphorylated with phospholipid, Ca²⁺-dependent protein kinase has been purified and the intrinsic specificity determined to reside in the catalytic subunit of the enzyme complex. Comparison with a preparation of pork heart protein phosphatase suggests that this specificity may be a general property of a class of protein phosphatases. Protein kinase C-phosphorylated histone H1 represents an improved substrate for phosphatase detection providing a five to tenfold greater sensitivity than other substrates including cAMP-dependent protein kinase phosphorylated H1.