After transfer of sugars to endogenous macromolecular acceptors, the enzyme converts nucleoside diphosphates to nucleoside monophosphates which in turn exit the Golgi lumen in a coupled antiporter reaction, allowing entry of additional nucleotide sugar from the cytosol. Has a role in cell wall morphogenesis during the transition of budding growth into hyphal growth, a process known as dimorphism. GDP + H2O = GMP + H(+) + phosphate Protein modification; protein glycosylation. Belongs to the GDA1/CD39 NTPase family.