The aim of this proposal is to understand how the mechanical properties of structural components within blood cells change with charging molecular structure and composition. We will use the human erythrocyte membrane to investigate the molecular basis of the mechanical behavior of cell membranes, and we will use marginal bands isolated from platelets and nucleated erythrocytes of non- mammalian vertebrates to study the structural properties of microtubular assemblies. The red cell membrane is an ideal system for studying the structure and mechanical function of cell membranes. The mechanical properties of the erythrocyte membrane are important in themselves because membrane elasticity plays a vital role in maintaining the viability of the cell in the circulation. These studies will make a direct contribution toward understanding the mechanics underlying hemolytic disorders by establishing the link between specific molecular lesions and cell destruction. Micromechanical experiments will be performed on individual cells to obtain measurements of intrinsic membrane mechanical properties. A new biophysical method will be used to measure changes in the association between the membrane bilayer and the membrane skeleton. The specific alterations in membrane structure to be investigated include naturally-occurring skeletal defects associated with the inherited disorders hereditary spherocytosis and hereditary elliptocytosis, as well as perturbations in skeletal organization produced by addition of proteolytic fragments of skeletal proteins to the membrane in vitro. Microtubules are ubiquitous structural components found in virtually every type of cell except the mammalian erythrocyte. In spite of their widespread occurrence as a major cytoskeletal element, little is known about the mechanical properties of micro- tubular structures or the regulation of those properties. Marginal bands isolated from human platelets and erythrocytes from fish and amphibians will be used to determine the relationship between the number of microtubules in the band and its structural properties. Single bands will be stretched against calibrated glass fibers and the force-deflection data pairs will be used to calculate both flexural and extensional rigidities of the bands. Interactions between exogenously added microtubule-associated proteins and marginal bands will be studied using fluorescence microscopy, and changes in structural properties caused by these interactions will be measured.