At least four types of the enzyme phosphodiesterase 4 (PDE4) are known:
PDE4A PDE4B PDE4C PDE4D
See also 3',5'-cyclic-AMP phosphodiesterase Phosphodiesterase (PDE) PDE4 inhibitor
Wikipedia
At least four types of the enzyme phosphodiesterase 4 (PDE4) are known:
PDE4A PDE4B PDE4C PDE4D
See also 3',5'-cyclic-AMP phosphodiesterase Phosphodiesterase (PDE) PDE4 inhibitor