第五型磷酸二酯酵素（Phosphodiesterase 5, PDE5）在細胞中扮演著調控 cGMP 濃度的重要角色，與男性陽萎有直接的相關性。Tadalafil，也稱為犀力士（Cialis），是一個B-carbolin衍生物能夠專一的抑制 PDE5 的活性。s

EC no.: 3.1.4.17

Functional Class: Hydrolase

FASTA Sequence

>1UDT:A|PDBID|CHAIN|SEQUENCE

TRELQSLAAAVVPSAQTLKITDFSFSDFELSDLETALCTIRMFTDLNLVQN
FQMKHEVLCRWILSVKKNYRKNVAYHNWRHAFNTAQCMFAALKAGK
IQNKLTDLEILALLIAALSHDLDHRGVNNSYIQRSEHPLAQLYCHSIMEH
HHFDQCLMILNSPGNQILSGLSIEEYKTTLKIIKQAILATDLALYIKRRGEF
FELIRKNQFNLEDPHQKELFLAMLMTACDLSAITKPWPIQQRIAELVATE
FFDQGDRERKELNIEPTDLMNREKKNKIPSMQVGFIDAICLQLYEALTHV
SEDCFPLLDGCRKNRQKWQALAEQQ

Overview of the PDE5 complex structures.
Stereo diagram of the human PDE5 structure: Ribbons
The catalytic domain of the PDE5 molecule can be divided into three subdomains: an N-terminal cyclin-fold domain (residues 537–678), a linker helical domain (residues 679–725) and C-terminal helical bundle domain (residues 726–860).
The bound tadalafil molecules is overlapped and shown as stick models.
The zinc and magnesium ions are represented.

Protein ID : 1UDU

參考資料：
Sung, B. J., Hwang, K. Y., Jeon, Y. H., Lee, J. I., Heo, Y.S., Kim, J. H., Moon, J., Yoon, J. M., Hyun, Y. L., Kim, E., Eum, S. J., Park, S.Y., Lee, J. O., Lee, T. G., Ro, S., Cho, J. M. (2003) Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules. Nature 425, 98-102.