Solute transport can be driven not only by the electrochemical gradi- ent but also by ATP hydrolysis. An unc (ATPase) mutant of Escherichia coli was unable to take up maltose under conditions where a large proton motive force was established, but the disaccharide was transported when the mutant was supplied with substrates that can produce ATP through substrate-level phosphorylation (Section 5.6.5) such as 1,3-diphosphoglycerate and phosphoenolpyruvate. Maltose transport requires not only ATP but also a binding protein in the periplasrn. Gra1n~negatiVe bacteria have solute-binding proteins in the pen’- plasm that are released when cells are subjected to osmotic shock with EDTA and MgC12 (cold osmotic shock). For this reason,