Protein kinase-phosphatase cascade second messenger

Phosphorylation by protein kinases of specific seryl, threonyl, or tyrosyl residues—and subsequent dephosphorylation by protein phosphatases—regulates the activity of many human enzymes. The protein kinases and phosphatases that participate in regulatory cascades which respond to hormonal or second messenger signals constimte a bio-organic computer that can process and integrate complex environmental information to produce an appropriate and comprehensive cellular response. 

The biological consequences of the interaction of pTyr-containing proteins with SH2-domain proteins depend on the function of the protein recruited. Thus, a phosphorylation-dephosphorylation cascade may be activated by recruitment of a kinase or a phosphatase, or a target enzyme maybe stimulated which produces a second messenger in response to a receptor signal,25 or signalling proteins may be relocated and transcription factors activated.26 Eventually, most of these events lead to the activation of gene transcription. 

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