What enzyme is inhibited by theophylline?

Theophylline is a methylxanthine that acts as a bronchodilator primarily through the inhibition of phosphodiesterase (PDE) enzymes. By inhibiting PDE, theophylline prevents the breakdown of cyclic AMP (cAMP), leading to increased levels of cAMP within cells. Elevated cAMP levels promote relaxation of smooth muscle in the airways, allowing for dilation and improved airflow, which is especially beneficial in the treatment of asthma and other respiratory conditions.

Phospholipase, cyclooxygenase, and aminopeptidase are not directly impacted by theophylline in the same way that phosphodiesterase is. Phospholipase is involved in the metabolism of phospholipids and the formation of arachidonic acid, which plays a role in inflammatory responses but is not the target of theophylline's action. Cyclooxygenase is mainly involved in the synthesis of prostaglandins, and aminopeptidase is an enzyme involved in protein metabolism. Therefore, these options do not represent the mechanism of action relevant to the use of theophylline.