State modifications of thymocyte plasma membrane proteins and lipids by mitogenic doses of concanavalin A: a Raman study on isolated membrane vesicles.

Sealed plasma membrane vesicles from rabbit thymocytes were reacted with 0.4-10 micrograms concanavalin A/ml, that is at concentrations that produce cooperative lectin-binding in vivo and in vitro and induce mitogenesis of intact cells. The effects of concanavalin A were monitored by laser Raman spectroscopy of the vesicles in the CH-stretching region. This technique revealed moderately cooperative lipid state transitions in untreated membranes centered at about -6 degrees and 25 degrees, as well as a protein state change at about 43 degrees C. Concanavalin A treatment of the membranes lowered the transition temperatures of the integral of 25 degrees an integral of 43 degrees state changes indicating a direct effect of lectin binding on membrane protein/lipid organization. It is proposed that the primary protein involved is the 55,000D transmembrane protein (Schmidt-Ullrich, R., Mikkelsen, R. B. and Wallach, D. F. H. (1978), J. Biol. Chem. 253, 6973-6978), known to be the high-affinity receptor for concanavalin A, and that the concanavalin A-sensitive integral of 25 degrees transition arises from lipids associated with this protein.