major classes of protein kinases Signal 1 Signal 2 Signal 3 Signal 4 Signal 5 Outside Receptor Receptor Recepto Receptor D//Receptor protein Membrane tyrosine kinase Inside CAMP CGMP Diacylglycerol X 不不 PKG Calmodulin PKC Protein Ser/Thr kinases Multifunctional Dedicated kinasesmajor classes of protein kinases