Margolis R N, Cardell R R, Curnow R T
J Cell Biol. 1979 Nov;83(2 Pt 1):348-56. doi: 10.1083/jcb.83.2.348.
A detailed investigation was conducted to determine the precise subcellular localization of the rate-limiting enzymes of hepatic glycogen metabolism (glycogen synthase and phosphorylase) and their regulatory enzymes (synthase phosphatase and phosphorylase phosphatase). Rat liver was homogenized and fractionated to produce soluble, rough and smooth microsomal fractions. Enzyme assays of the fractions were performed, and the results showed that glycogen synthase and phosphorylase were located in the soluble fraction of the livers. Synthase phosphatase and phosphorylase phosphatase activities were also present in soluble fractions, but were clearly identified in both rough and smooth microsomal fractions. It is suggested that the location of smooth endoplasmic reticulum (SER) within the cytosome forms a microenvironment within hepatocytes that establishes conditions necessary for glycogen synthesis (and degradation). Thus the location of SER in the cell determines regions of the hepatocyte that are rich in glycogen particles. Furthermore, the demonstration of the association of synthase phosphatase and phosphorylase phosphatase with membranes of SER may account for the close morphological association of SER with glycogen particles (i.e., disposition of SER membranes brings the membrane-bound regulatory enzymes in close contact with their substrates).
开展了一项详细研究，以确定肝糖原代谢限速酶（糖原合酶和磷酸化酶）及其调节酶（合酶磷酸酶和磷酸化酶磷酸酶）的确切亚细胞定位。将大鼠肝脏匀浆并分级分离，以产生可溶性、粗面和滑面微粒体级分。对这些级分进行酶活性测定，结果表明糖原合酶和磷酸化酶位于肝脏的可溶性级分中。合酶磷酸酶和磷酸化酶磷酸酶活性也存在于可溶性级分中，但在粗面和滑面微粒体级分中均能明确鉴定到。提示滑面内质网（SER）在细胞质内的位置在肝细胞内形成了一个微环境，该微环境为糖原合成（及降解）建立了必要条件。因此，SER在细胞内的位置决定了肝细胞中富含糖原颗粒的区域。此外，合酶磷酸酶和磷酸化酶磷酸酶与SER膜的关联证明，可能解释了SER与糖原颗粒紧密的形态学关联（即SER膜的分布使膜结合调节酶与其底物紧密接触）。
