the purified kinase undergoes an autocatalytic reaction resulting in the specific phosphorylation of the beta subunit , exhibits a low apparent km for both atp and gtp as nucleoside triphosphate donor ( 17 and 66 microm , respectively ) , phosphorylates both casein and phosvitin but neither histones nor protamine , modifies both serine and threonine residues in casein , and is strongly inhibited by heparin ( i50 = 21 ng/ml ) .
C0031727
kinase
C0031715
phosphorylation