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Unformatted text preview: The phosphorylation of proteins by a specific enzyme (a protein kinase ) is a widespread cellular mechanism for regulating protein activity. Most protein kinases act on other substrate proteins, unlike tyrosine kinases that act on themselves. Most phosphorylation occurs at either serine or threonine amino acids of the substrate protein (unlike tyrosine phosphorylation in tyrosine kinases). Many of the relay molecules in a signal-transduction pathway are protein kinases that act on other protein kinases to create a phosphorylation cascade. Each protein phosphorylation leads to a conformational change because of the interaction between the newly added phosphate group and charged or polar amino acids on the protein. Phosphorylation of a protein typically converts it from an inactive form to an active form....
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- Fall '10