An NH2-terminal truncated cytochrome P450 CYP3A4 showing catalytic activity is present in the cytoplasm of human liver cells.
Cytochrome P450 3A4 (CYP3A4), is the dominant human liver hemoprotein enzyme localized in the endoplasmic reticulum (ER), and is responsible for the metabolism of more than 50% of clinically relevant drugs. While we were studying CYP3A4 expression and activity in human liver, we found that anti-CYP3A4 antibody cross-reacted with a lower band in liver cytoplasmic fraction. We assessed the activities of CYP3A4 and its truncated form in the microsomal and cytoplasmic fraction, respectively. In the cytoplasmic fraction, truncated CYP3A4 showed catalytic activity when reconstituted with NADPH-cytochrome P-450 reductase and cytochrome b5. In order to determine which site was deleted in the truncated form in vitro, we transfected cells with N-terminal tagged or C-terminal tagged human CYP3A4 cDNA. The truncated CYP3A4 is the N-terminal deleted form and was present in the soluble cytoplasmic fraction. Our result shows, for the first time, that N-terminal truncated, catalytically active CYP3A4 is present principally in the cytoplasm of human liver cells.
Jeon
Songhee
S
Department of Dermatology, Dongguk University School of Medicine, Goyang 410-773, Korea.
Kim
Keon Hee
KH
Yun
Chul Ho
CH
Hong
Boo-Whan
BW
Chang
Yoon-Seok
YS
Han
Ho-Seong
HS
Yoon
Yoo-Seok
YS
Choi
Won-Bum
WB
Kim
Soyun
S
Lee
Ai-Young
AY
D015153:Blotting, Western; D002384:Catalysis; D002460:Cell Line; D051544:Cytochrome P-450 CYP3A / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology*; D006801:Humans; D008862:Microsomes, Liver / Q000201:enzymology*
D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human