Characterization of two casein kinase activities in the fungus Mucor rouxii

Two cyclic-nucleotide independent soluble casein kinase activities (CK I and CK II) from the fungus Mucor rouxii have been isolated, characterized and found to fit in the general classification of type 1 (CK I) and 2 (CK II) casein kinases, according to their enzymatic and structural properties. Both enzymes phosphorylate acidic substrates, require Mg2+ and have a chromatographic behaviour on DEAE-Sepharose and phosphocellulose similar to their mammalian counterparts. CK I has a sedimentation coefficient of 3.5 S, uses ATP as a phosphate donor (Km = 40 microM), phosphorylates casein mainly on serine residues, its activity is strongly inhibited by KCl and polyamines. CK II has a sedimentation coefficient of 7.4 S, uses ATP and GTP as phosphate donors (Km ATP = 10 microM; Km GTP = 40 microM), phosphorylates casein in serine and threonine, its activity is stimulated by KCl and by polyamines and is inhibited by heparin (I50 = 0.5 micrograms/ml). Casein kinase activity associated to particulate fraction (40% of total) has been partially characterized and shown to be similar to the soluble CK I activity.