Figure 9.

Model for UDP-Glc metabolism in Golgi vesicles. UDP-Glc is transported into the lumen of Golgi cisternae, Glc is immediately transferred to polymers at different stages of growth, and UDP is released. However, this product is immediately hydrolyzed by Golgi UDPase, producing UMP and Pi. Although a pool of both metabolites can be observed in the Golgi cisternae, they do not accumulate and instead exit the Golgi cisternae. The exit of UMP is stimulated by UDP-Glc, suggesting an exchange mechanism, whereas Pi exits the Golgi cisternae by an independent mechanism.