K252a is a potent and selective inhibitor of phosphorylase kinase

The inhibition of phosphorylase kinase by a number of protein kinase inhibitors was examined. Both K252a and staurosporine are potent inhibitors of phosphorylase kinase with IC50 values of 1.7 nM and 0.5 nM respectively. K252a shows a 300-fold selectivity for this enzyme over protein kinase C whereas staurosporine shows only a 20-fold selectivity for phosphorylase kinase. In contrast, the Roche bis-indolyl maleimides inhibit phosphorylase kinase with IC50 values of approximately 1 microM and are highly selective for protein kinase C.