This project is comprised of research into the structure and functioning of ion transport systems. There are currently two active subprojects: (1) Transient kinetics: A collaborative study with Froehlich and Fendler.on the source of the transmembrane current that is generated by phosphorylation of the sodium pump has been completed. Collaboration with Froehlich on the source of the biphasic characteristics of phosphorylation and dephosphorylation is continuing. (2) Investigation of posttranslational modifications of the sodium pump. This project involves characterization of identified fragments of the sodium pump catalytic subunit by mass spectrometry.