Single replacement constructs of all hydroxyl, basic, and acidic amino acids identify new function and structure-sensitive regions of the mitochondrial phosphate transport protein.

The phosphate transport protein (PTP) catalyzes the proton cotransport of phosphate into the mitochondrial matrix. It functions as a homodimer, and thus residues of the phosphate and proton pores are somewhat scattered throughout the primary sequence. With 71 new single mutation per subunit PTPs, all its hydroxyl, basic, and acidic residues have now been replaced to identify these essential residues.