Shears S B, Evans W H, Kirk C J, Michell R H
Department of Biochemistry, University of Birmingham, U.K.
Biochem J. 1988 Dec 1;256(2):363-9. doi: 10.1042/bj2560363.
Previous studies have shown that most of the inositol 1,4,5-trisphosphate/inositol 1,3,4,5-tetrakisphosphate 5-phosphatase activity of rat hepatocytes is associated with the plasma membrane [Shears, Parry, Tang, Irvine, Michell & Kirk (1987) Biochem. J. 246, 139-147]. We now show that the specific activity of this enzyme is highest in the bile-canalicular domain of the plasma membrane, at the opposite pole of the hepatocyte from the presumed site of receptor-mediated formation of inositol 1,4,5-trisphosphate. In intact hepatocytes and in sealed membrane vesicles originating from the bile-canalicular domain of the plasma membrane, the 5-phosphatase activity was mostly latent and therefore located at the cytoplasmic surface. A substantial amount of 5-phosphatase was also found in rat liver endosomal fractions, particularly a 'late' endosomal subfraction, indicating that this enzyme may be transported between the sinusoidal plasma membrane and other cellular membranes.
先前的研究表明，大鼠肝细胞中大部分肌醇1,4,5-三磷酸/肌醇1,3,4,5-四磷酸5-磷酸酶活性与质膜相关[希尔斯、帕里、唐、欧文、米歇尔和柯克（1987年）《生物化学杂志》246卷，第139 - 147页]。我们现在表明，这种酶的比活性在质膜的胆小管区域最高，该区域位于肝细胞与推测的受体介导的肌醇1,4,5-三磷酸形成位点相对的另一端。在完整的肝细胞以及源自质膜胆小管区域的密封膜泡中，5-磷酸酶活性大多处于潜伏状态，因此位于细胞质表面。在大鼠肝脏内体组分中也发现了大量的5-磷酸酶，特别是一个“晚期”内体亚组分，这表明该酶可能在窦状质膜和其他细胞膜之间转运。
