Control of Enzyme Activity by Phosphorylation

One of the most common control mechanisms for enzymes is by phosphorylation. The side-chain hydroxyl groups of serine, threonine, and tyrosine can all form phosphate esters. Transport across membranes provides an important example, such as the sodium-potassium ion pump, which moves potassium into the 

Chapter 7 The Behavior of Proteins Enzymes, Mechanisms, and Control 

Many examples appear in processes involved in generating enei, as is the case in carbohydrate metabolism. Glycogen phosphorylase, which catalyzes the 

Does phosphorylation always increase enzyme activity  

Although it would be convenient to have a model in which phosphorylation always increases the activity of an enzyme, biochemistry is not so kind to us. In reality, we cannot predict whether phosphorylation will increase or decrease the activity of an enzyme. In some systems, the effects on two opposing enzymes are coordinated. For example, a key enzyme in a catabolic pathway may be activated by phosphorylation while its counterpart in an anabolic opposing pathway is inhibited by phosphorylation. 

---