Responses to fast-acting hormones by covalent modification of enzyme proteins

3 Responses to fast-acting hormones by covalent modification of enzyme proteins 

The hormonal regulation of glycogen synthesis and utilization is one of the best understood of such mechanisms. Two enzymes are involved, and obviously it is not desirable that both enzymes should be active at the same time  

In response to insulin (secreted in the fed state) there is increased synthesis of glycogen and inactivation of glycogen phosphorylase. In response to glucagon (secreted 

There is a further measure of instantaneous control by intracellular metabolites which can over-ride this hormonal regulation  

A cell will respond to a fast-acting hormone only if it has cell-surface receptors that bind the hormone. The receptors are transmembrane proteins at the outer face of the membrane they have a site which binds the hormone, in the same way as an enzyme binds its substrate, by non-covalent equilibrium binding. 

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