The parasitic protist Trichomonas vaginalis is the causative agent of trichomoniasis, a highly prevalent sexually transmitted infection. The organism is known to accumulate substantial deposits of the polysaccharide glycogen, which is believed to serve as a store of carbon and energy that can be tapped during periods of nutrient limitation. Such nutrient limitation is likely to occur when T. vaginalis is transmitted between hosts, implying that glycogen may play an important role in the lifecycle of the parasite. Both T. vaginalis glycogen synthase and glycogen phosphorylase, key enzymes of glycogen synthesis and degradation, respectively, have been cloned and characterized, and neither enzyme is subject to the post-translational controls found in other, well-characterized eukaryotic systems. Thus, it is unclear how glycogen metabolism is regulated in this organism. Here we use a glucose limitation/re-feeding protocol to show that the activities of key enzymes of glycogen synthesis do not increase during re-feeding when glycogen synthesis is stimulated. Rather, a simple model appears to operate with glycogen storage being driven by the extracellular glucose concentration.

寄生性原生生物阴道毛滴虫是毛滴虫病的病原体，毛滴虫病是一种非常普遍的性传播感染。已知该生物体会积累大量多糖糖原沉积物，据信多糖糖原可作为碳和能量的储存库，可在营养受限期间加以利用。当阴道毛滴虫在宿主之间传播时可能会发生这种营养限制，这意味着糖原可能在寄生虫的生命周期中发挥重要作用。这两种阴道毛滴虫糖原合成酶和糖原磷酸化酶分别是糖原合成和降解的关键酶，已被克隆和表征，并且这两种酶都不受在其他已充分表征的真核系统中发现的翻译后控制的影响。因此，尚不清楚该生物体中如何调节糖原代谢。在这里，我们使用葡萄糖限制/重新喂养方案来表明，当糖原合成受到刺激时，糖原合成关键酶的活性在重新喂养期间不会增加。相反，一个简单的模型似乎与由细胞外葡萄糖浓度驱动的糖原储存一起运行。