Sar1/Arf refers to a family of small GTP-binding proteins that play crucial roles in intracellular transport and membrane trafficking. These proteins are involved in the formation of vesicles that transport proteins and lipids between different cellular compartments, such as the endoplasmic reticulum and the Golgi apparatus. The Sar1 protein is primarily associated with the initiation of vesicle budding from the endoplasmic reticulum, while Arf proteins are involved in the formation of vesicles from the Golgi apparatus. Both proteins act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state to regulate their functions in cellular processes.