A molecular order in the synthesis and degradation of glycogen in the liver.
A molecular order in the synthesis and degradation of glycogen in the liver.
复制标题
肝脏中糖原合成和降解的分子顺序。
DOI：
--
复制
发表时间：
1979
期刊：
影响因子：
--
通讯作者：
H. Hers
中科院分区：
文献类型：
--
作者：
P. Devos;H. Hers
当喂食禁食大鼠或小鼠时，肝糖原以约1%/h的线性速率合成约6 h。给予放射性前体，通常是β '4C]半乳糖，允许脉冲标记在开始再喂养后不同时间形成的糖原。在给予标记后不久，放射性葡糖基单元优先位于糖原的外链上。一个几乎相等的分布之间的内链和外链达到后，随着预先存在的糖原量的增加而增加的时间。后来，放射性分子没有进一步扩大，尽管糖原的质量增加了三倍。在麻醉大鼠体内或体外分离的肝细胞和由伴刀豆球蛋白A分离的酶-糖原复合物组成的无细胞系统中，诱导了在再喂养开始后不同时间标记的糖原降解。在所有这些条件下，最后结合的放射性单位首先被释放，反之亦然。这种有序的降解不能用最初的外链去除来解释。在伴刀豆球蛋白-A结合糖原，有序降解是不太明显时，该制剂已提交高速离心，剧烈匀浆，超声波处理或暴露于洗涤剂。在哺乳动物肝脏中，糖原以直径约为0.1 μ m的糖原的形式存在[I]。这些大结构也被称为α颗粒糖原，由称为β颗粒的亚基组成[2]。β亚基的大小（直径15-30 nm）和一般外观与肌肉和大多数其他哺乳动物细胞中的糖原颗粒相似;它们可能对应于由内链和外链组成的分支结构，目前被认为是糖原分子。基于颗粒尺寸和糖原密度的计算允许对分子量进行非常粗略的估计;它们产生的β亚基值为4 x lo 6，α颗粒值为400 x lo 6 [3]。超微粒子研究[4- 61]给出了非常不同的数值，并指出存在一小部分质量可能是α粒子质量数倍的超大结构。目前尚不清楚β亚基是否是
When fasted rats or mice were refed, liver glycogen was synthesised at a linear rate of approximately 1 %/h for a period of about 6 h. The administration of a radioactive precursor, usually ['4C]galactose, allowed pulse labelling of the glycogen formed at various times after the initiation of refeeding. Soon after the administration of the label, the radioactive glucosyl units were preferentially located on the outer chains of glycogen. An almost equal distribution between the inner and outer chains was attained after a time which increased with increasing amounts of preexisting glycogen. Later on, the radioactive molecules were not further enlarged although the mass of glycogen increased threefold. The degradation of the glycogen that had been labelled at various times after initiation of refeeding was induced either in vivo in anesthetized rats, or in vitro in isolated hepatocytes and in a cell-free system made up of the enzyme-glycogen complex as isolated by concanavalin A. Under all of these conditions, the radioactive units that were incorporated last were liberated first and vice versa. This ordered degradation could not be explained by the initial removal of outer chains. In the concanavalin-A-bound glycogen, the ordered degradation was much less apparent when the preparation had been submitted to high-speed centrifugation, vigorous homogenization, ultrasonic treatment or exposure to detergents. In the mammalian liver, glycogen is present in the form of rosettes the diameter of which approximates 0.1 pm [I]. These large structures have also been called alpha-particulate glycogen and are made up of subunits termed beta particles [2]. The beta subunits are similar in size (diameter 15-30 nm) and general appearance to the particles of glycogen seen in muscle and in most other mammalian cells; they presumably correspond to the branched structure, made of inner and outer chains, which is currently considered as a glycogen molecule. Calculations based on the dimension of the particles and on the density of glycogen allowed a very rough estimation of the molecular weight ; they yielded values of the order of 4 x lo6 for the beta subunit and of 400 x lo6 for the alpha particles [3]. Ultracentrifugal studies [4- 61 have given very divergent values and have indicated the presence of a small percentage of extremely large structures the mass of which could be several times that of an alpha particle. It is not known at the present time whether or not the beta subunits are