中文摘要
　　細胞色素P450這個超級家族為含鐵基質硫醇類蛋白酵素，對許多存在於生物體內的內生性化合物氧化、過氧化及還原代謝過程及外來物質的生物轉化(biotransformation)作用扮演著重要的角色。其中CYP3A次家族，是細胞色素這超級家族在肝臟中表現量最多的次家族，也是目前約50%臨床用藥及內生性固醇物質的主要代謝酵素。
CYP3A次家族共含有四個成員：CYP3A4、CYP3A5、CYP3A7 及CYP3A43。CYP3A4主要表現在肝臟及小腸中，而CYP3A5主要表現在腎臟、結腸…等肝外組織，此外CYP3A5在個體間表現量的差異頗大，而此差異性多源自於基因多型性的關係，基因多型CYP3A5*3的存在會導致組織中CYP3A5的表現量減低許多。
　　CYP3A5與CYP3A4在受質選擇上具有相當的重疊性，常以midazolam當指示藥物去區別CYP3A5與CYP3A4的代謝能力。在我們實驗室先前研究發現，CYP3A5*3基因組態會影響CYP3A5在組織中的表現程度，但對midazolam在個體體內的代謝情形卻是沒有影響，相同的情況也在其他學著的研究中發現。此外，2000年Lin等人指出，基因組態為同型合子CYP3A5*3的個體，在其空腸中CYP3A4的表現量似乎有較異型合子CYP3A5*1/*3的個體來的高。因此本實驗的目的即在探討，是否CYP3A4和CYP3A5間也透過特殊的調控機制，而致CYP3A4的表現量會因應不同的CYP3A5表現量而有所改變。
　　實驗結果顯示，無論在模擬小腸(Caco-2)或是肝臟(HepG2)的細胞體外模式下，CYP3A4酵素在mRNA及蛋白質的表現量並不會因應不同的CYP3A5表現量而有所改變。

Abstract
　　The cytochrome P450 (CYP) proteins are heme-containing enzymes and catalyze primarily oxidations of endobiotics and xenobiotics. The CYP3A subfamily is the most abundantly expressed P450 in human liver, and four CYP3A genes, CYP3A4, CYP3A5, CYP3A7, CYP3A43, have been identified. CYP3A4 is predominantly expressed in human liver and intestine. CYP3A5 is mainly expressed in the intestine and kidney and it is known that polymorphic CYP3A5 expression is strongly correlated with a single nucleotide polymorphism CYP3A5*3, A→G, within intron 3 of the CYP3A5 gene, which resulted in absence of CYP3A5.
　　Because the overlapping substrate specificity between CYP3A4 and CYP3A5, midazolam is often used as a probe drug to delineate the metabolic activity of the two enzymes. In our previously study, we have showed that the CYP3A5*3 genotype affects the level of CYP3A5 but does not influence the midazolam metabolism in vivo. And Lin et al. also pointed that the CYP3A4 level seemed to be up-regulated in homozygous CYP3A5*3 subjects. The aim of this study is to see whether the expression level of CYP3A4 may be affected by the level of CYP3A5 or not.
　　In the present data, CYP3A5 did not influence CYP3A4 expression even in mRNA level or protein level. And the reason why the metabolism of midazolam showed no differences between subjects of different CYP3A5 genotypes remains to be elucidated.

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