Platelet Protein Phosphorylation

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Abstract
Over the last decade phosphorylation of proteins has emerged as a critical mechanism in the control of intracellular processess within platelets and many other cells.1,2 It is pertinent to ask why this should be? There are probably two major reasons. First the addition of the phosphate group to a protein adds, though a fairly simple reaction, a substituent group which can substantially change the character of the protein, its conformation and its interactions with ions and with other proteins. Thus, for example, an inactive enzyme can become an active one after receiving a phosphate group, or vice versa. A second principle reason is that the addition of a phosphate group is readily reversible through the action of phosphatases within cells, to allow quick control over the active state of the protein. Just as phosphorylation of a protein may be associated with either activation or inhibition, so phosphorylation reactions can mediate either activation or inhibition of cellular function.