State Modifications of Thymocyte Plasma Membrane Proteins and Lipids by Mitogenic Doses of Concanavalin A: A Raman Study on Isolated Membrane Vesicles

Abstract

Sealed plasma membrane vesicles from rabbit thymocytes were reacted with 0.4–10 μg 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 concanaval in 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° and 25°, as well as a protein state change at about 43°C. Concanavalin A treatment of the membranes lowered the transition temperatures of the ~ 25° and ~ 43° 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 ~ 25° transition arises from lipids associated with this protein.