This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The RBC membrane is not a static but a metabolically regulated active structure. It is known that biochemical energy controls its static and dynamic characteristics. The presence of ATP is not only crucial in maintaining the biconcave shape of the RBC membrane, but was also shown to increase the dynamic membrane fluctuations. However, the regulatory mechanism of ATP in RBC membranes still remains elusive. We investigate the effects of ATP by measuring the morphologies and membrane dynamics of RBC using the quantitative phase microscopes we developed.