High-Pressure Stopped-Flow Studies to Characterize Transient Conformational Transitions of a Membrane Enzyme: Na, K-ATPase

摘要

The kinetics of ATP-induced phosphorylation and K~+ binding of Na,K-ATPase has been investigated at different pressures by applying the fluorescence stopped-flow method For both type of reactions, a conforma-tional transition is considered to act as rate-limiting reaction step. These transitions are characterized by large activation volumes up to +100 ml mol~(-1). The significance of the determined values in terms of Kramers' theory is discussed. A molecular interpretation related to solvation changes and cavity formation in the transmembrane domain of the protein is suggested. A large negative reaction volume is found upon ATP binding (-100 ml mol~(-1)). The selective binding of Na~+ and K~+ leads to smaller, but positive values.