薬物代謝酵素の分子多型と機能発現に関する研究

抄録

Liver microsomal carboxylesterases (CES) function in the hydrolysis of a wide variety of endogenous and xenobiotic compounds, and play an important role in drug and lipid metabolism in many mammalian species. For past three decades, we have undertaken the diverse studies on CES from the view points of enzymology and drug metabolism. First, we have purified twenty-seven CES isozymes to electrophoretic homogeneity from liver microsomes of ten mammalian species and humans, and their physical, enzymological and immunological properties were compared each other. The CES isozymes from various species examined showed considerable similarities in physicochemical and immunological properties, but not similar in substrate specificities. Ramda Zap II library from mouse liver, and λ gt 11 libraries from human and rat liver were screened with antibodies raised to a purified liver CES isozymes. The deduced amino acid sequence of the clone possessed many structural characteristics that are highly conserved among rat RL1, RH1, RHlec, RS1 and RS2, mouse ML1, MH1, MS1 and human HU1, including active site sequence (GESAGG, NKQEXG, GDHXD), and four cysteines which may be involved in the specific disulfide bond. It is well known that proteins which are retained in the endoplasmic reticulum lumen contain the retention signal at their carboxyl-terminal of the tetrapeptide. The five CES clones (RL1, RH1, RHlec, MH1 and HU1) also contained ER-retention signal (HXEL). When clone was expressed in COS cells, the plasmid-coded protein was retained. The cells expressing CES were found to have very highly activity towards xenobiotic esters and amides. In conclusion, liver microsomal CES in mammalian and humans are closely involved in drug and lipid metabolism in the endoplasmic reticulum, and it is noteworthy that the isozymes from various species examined showed considerable similarities in amino acid sequences, but not similar in substrate specificities. These reasons may be, at least in part, due to the variances of substrate binding site.