G-binding proteins

[slaper14]

The hydrolysis of GTP to GDP is slow in some enzymes and fast in others. Why wouldn't every enzyme evolved to hydrolyse the GTP as fast as possible. What qualities would a slow G-protein bestow upon a pathway?

The exchange of GTP for the GDP is slow and must be enhanced by addition proteins that are regulated. What selective advantage would this requirement provide for the cell?

[JackBean]

because those proteins can work in dependence of GTP-binding. Thus, if they hydrolyse that slowly, they work longer. And on the other hand, when they hydrolyse GTP to GDP, they stop working and unless it's exchanged for new GTP, they are not active (= regulation).