Rothman-Denes L B, Cabib E
Proc Natl Acad Sci U S A. 1970 Jul;66(3):967-74. doi: 10.1073/pnas.66.3.967.
The glycogen content of yeast rises dramatically just before the onset of the stationary phase of growth. Concomitantly, a rapid increase was found in the glucose 6-phosphate-independent (I) activity of glycogen synthetase, as well as in the total amount of enzyme. A mutant (GS 1-36) was obtained, which did not accumulate glycogen during growth. The synthetase from this strain was in the glucose 6-phosphate-dependent (D) form at all times. The total enzymatic activity of the mutant also increased sharply at the end of the logarithmic phase, although its maximal value was only one third that of the parent strain. Incubation with glucose of wild type resting cells from the logarithmic phase resulted in a slow accumulation of glycogen, which was accelerated after 20 min. At the same time a transformation from the D to I form of the enzyme was detected. The same slow initial rate of glycogen deposition was found with stationary cells of mutant GS 1-36, but the rate gradually declined to zero, rather than accelerating. The interconversion of the I and D forms was obtained with extracts from cells harvested during different phases of growth. Examination of the properties of the I and D forms showed that the latter was much more strongly inhibited by ATP at low glucose 6-phosphate concentration. These findings clearly establish the fundamental role of the I form in glycogen accumulation. When taken together with previous results, they also show that the physiological significance of the I-D interconversion depends on the concentration of glucose 6-phosphate. Under certain conditions glucsoe 6-phosphate appears to regulate directly the activity of the predominant form of the enzyme.
酵母中的糖原含量在生长静止期开始前会急剧上升。与此同时，发现糖原合成酶的6-磷酸葡萄糖非依赖性（I）活性以及酶的总量迅速增加。获得了一个突变体（GS 1-36），其在生长过程中不积累糖原。该菌株的合成酶始终处于6-磷酸葡萄糖依赖性（D）形式。突变体的总酶活性在对数期末也急剧增加，尽管其最大值仅为亲本菌株的三分之一。对数期野生型静息细胞与葡萄糖一起孵育会导致糖原缓慢积累，20分钟后加速。同时检测到酶从D形式向I形式的转变。突变体GS 1-36的静止细胞也发现了相同的缓慢初始糖原沉积速率，但该速率逐渐降至零，而不是加速。I和D形式的相互转化可通过在不同生长阶段收获的细胞提取物获得。对I和D形式特性的研究表明，在低6-磷酸葡萄糖浓度下，后者受到ATP的抑制作用更强。这些发现清楚地确立了I形式在糖原积累中的基本作用。与先前的结果结合起来看，它们还表明I-D相互转化的生理意义取决于6-磷酸葡萄糖的浓度。在某些条件下，6-磷酸葡萄糖似乎直接调节该酶主要形式的活性。
