HOW DOES THE PLANT PLASMA-MEMBRANE H+-ATPASE PUMP PROTONS

The plasma membrane H+-ATPase couples ATP hydrolysis to proton transport thereby establishing the driving force for solute transport into and out of plant cells. As such, this enzyme participates in a number of cellular processes important to the overall physiology of plants. From biochemical studies and the recent application of molecular approaches, the enzyme reaction mechanism and structure of this protein have been characterized. However, our basic understanding of how this enzyme links the endergonic reaction of ATP hydrolysis to proton translocation is far from complete. In this review, several significant questions regarding the energy coupling mechanism will be addressed in terms of information available on the plant plasma membrane H+-ATPase and from studies on other P-type transport ATPases. These questions focus on the chemical nature of proton translocation, how this is linked or driven by the ATP hydrolysis reaction and what role, if any, K+ has in the transport process.