Common mechanisms for enzyme-catalyzed bisubstrate reactions

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PI-3 kinase was first identified in studies of the 

polyoma virus, a DNA virus

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PKB contains:

A PH domain

A kinase domain

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PH domain of PKB binds with high affinity to the 

3-phosphates in both PI(3,4)P2 and PI(3,4,5)P3

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In unstimulated cells, 

concentration of phosphoinositides is low, and PKB is

inactive because its PH domain physically blocks the kinase active site

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Ligand-induced receptor activation,

Concentration of PI 3-phosphates rises

PH domain of PKB binds to PI 3-phosphates

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Maximal activation of PKB depends on recruitment to the cytosolic surface of the plasma membrane of two other kinases -PDK1 and PDK2.