Chen K S, Lardy H A
J Biol Chem. 1985 Nov 25;260(27):14683-8.
Glycogen synthesis from various combinations of substrates by hepatocytes isolated from rats fasted 24 h was studied. As reported by Katz et al. (Katz, J., Golden, S., and Wals, P. A. (1976) Proc. Natl. Acad. Sci. U. S. A. 73, 3433-3437), appreciable rates of glycogen synthesis occurred only in the presence of gluconeogenic precursors and one of several amino acids, which includes L-glutamine. L-Leucine had negligible effects on glycogen synthesis from 20 mM dihydroxyacetone and/or 15 mM glucose when L-glutamine was not added to the medium. In the presence of 10 mM L-glutamine, L-leucine greatly increased glycogen synthesis from these substrates. alpha-Ketoisocaproate was ineffective, as was oleate. NH4Cl depressed glycogen synthesis from 10 mM glucose plus 20 mM dihydroxyacetone in the absence of added L-glutamine and enhanced that in its presence, but these effects were weak compared to those of L-leucine. The amino acid analogues L-norvaline and L-norleucine exerted effects that were similar to those exerted by L-leucine. Under all conditions studied, cycloheximide and puromycin inhibited net glycogen synthesis. Cycloheximide did not stimulate gluconeogenesis from dihydroxyacetone, or phosphorylase in hepatocytes from starved rats, or glycogenolysis in hepatocytes from fed rats. Puromycin, however, stimulated glycogenolysis in hepatocytes from fed rats. Glycogen synthesis from 20 mM dihydroxyacetone proceeds with a pronounced initial lag phase that can be shortened by incubation of cells with glutamine plus leucine before addition of dihydroxyacetone. Concurrent measurements of glycogen synthesis, glycogen synthase, and gluconeogenesis under different conditions reveal that in addition to protein synthesis, activation of glycogen synthase, which must occur to allow glycogen synthesis in hepatocytes, requires a second component which can be satisfied by addition of dihydroxyacetone or fructose to the cells.
研究了从禁食24小时的大鼠分离出的肝细胞利用各种底物组合进行糖原合成的情况。正如卡茨等人所报道的（卡茨，J.，戈尔登，S.，和沃尔斯，P. A.（1976年）《美国国家科学院院刊》73，3433 - 3437），只有在糖异生前体和几种氨基酸之一（包括L - 谷氨酰胺）存在的情况下，糖原合成才会有可观的速率。当培养基中不添加L - 谷氨酰胺时，L - 亮氨酸对由20 mM二羟基丙酮和/或15 mM葡萄糖进行的糖原合成影响可忽略不计。在存在10 mM L - 谷氨酰胺的情况下，L - 亮氨酸极大地增加了从这些底物的糖原合成。α - 酮异己酸无效，油酸也是如此。在不添加L - 谷氨酰胺时，NH4Cl抑制了由10 mM葡萄糖加20 mM二羟基丙酮进行的糖原合成，而在其存在时则增强了糖原合成，但与L - 亮氨酸的作用相比，这些作用较弱。氨基酸类似物L - 正缬氨酸和L - 正亮氨酸产生的作用与L - 亮氨酸相似。在所有研究的条件下，放线菌酮和嘌呤霉素都抑制糖原的净合成。放线菌酮不刺激二羟基丙酮的糖异生，也不刺激饥饿大鼠肝细胞中的磷酸化酶，或喂食大鼠肝细胞中的糖原分解。然而，嘌呤霉素刺激喂食大鼠肝细胞中的糖原分解。由20 mM二羟基丙酮进行的糖原合成有明显的初始滞后阶段，在添加二羟基丙酮之前用谷氨酰胺加亮氨酸孵育细胞可缩短该滞后阶段。在不同条件下同时测量糖原合成、糖原合酶和糖异生表明，除了蛋白质合成外，糖原合酶的激活（这是肝细胞中进行糖原合成所必需的）还需要第二个成分，添加二羟基丙酮或果糖到细胞中可以满足这一成分需求。
