Non-selective inhibition of mammalian protein kinases by flavinoids in vitro

In vitro, the flavinoids quercetin, morin, and rutin produced comparable inhibition of protein kinase C prepared from bovine brain, the epidermal growth factor (EGF)-stimulated tyrosine specific protein kinase associated with A431 cell membranes, and the cAMP-stimulated protein kinase activity associated with rat brain tubulin. Concentrations producing 50% inhibition (IC50's) were in the 10 microM range. These findings demonstrate the lack of specificity of the flavinoids toward cyclic nucleotide-dependent vs cyclic nucleotide-independent protein kinases.