Phospholipids as the molecular instruments of ion and solute transport in biological membranes (phospholipid-mediated transport/modulators of transport/protein-constrained phospholipid/phospholipid-dependent enzymes)

Partition studies have established that phos- pholipids generally have the capabilities to mediate the trans- membrane transport of the full range of ions and solutes that physiologically cross biological membranes. The list of trans- portable species includes cations, anions, amino acids, citric acid cycle intermediates, nucleotides, and sugars. Phospho- lipid-mediated transport can be readily modulated by altering the phospholipid mixture or by addition of detergents, nucleo- tides, divalent metals, proteins, peptides, or ring compounds. Containment of phospholipid within channels in protein ap- pears to be the precondition for the formation of the micellar structure requisite for solute transport. Phospholipid-mediated transport is postulated to be a central feature of energy coupling, membrane-spanning systems, and membrane-bound, phos- pholipid-requiring enzymes.