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Figure 6. Different types of active transport systems. Left, the phosphoenolpyruvate carbohydratephosphotransferase system, found in bacteria only, is a multi-component system that catalyzes vectorial phosphorylation of certain sugars. Also plays important role in regulation of metabolism (catabolite repression). Middle, lac permease, an example of ion-gradient driven active transport on which we will concentrate. Right, ATP Binding Cassette (ABC) systems in which ATP hydrolysis is the driving force for transport. May function as multi-component systems with a periplasmic binding protein or with components fused in different combinations. These bacterial transport ATPases are homologous to eucaryotic ABC transporters involved in cystic fibrosis (CFTR) and multi-drug resistance (MDR).