Low- and high-affinity concanavalin a binding to thymocyte plasma membrane vesicles.

Binding of concanavalin A to isolated thymocyte membrane vesicles occurs through (a) numerous (approximately 6 x 106/cell equivalent) low-affinity sites (Ka = 1.3 x 105M-1) anf (b) fewer (approximately 0.4 x 106/cell equipment) specific receptors (Ka = 6.8 x 106 M-1) defined as 55,000 D glycoprotein and its multimers. Specific binding is positively-cooperative, with a Hill coefficient of approximately 1.8. Low concentrations of glutaraldehyde selectively crosslink the 55,000 D glycoprotein with replacement of positively-cooperative sites by high-affinity sites. It is proposed that concavalin A-binding induces multimerization of the 55,000 D glycoprotein.