High and low affinity binding sites for Concanavalin A on normal human fibroblasts in vitro

Abstract

The binding of high specific activity, radioactive Concanavalin A to cultured normal human fibroblasts was investigated. We report the presence of two classes of Concanavalin A binding sites on the plasma membranes of these cells. These classes of binding sites are distinguished by their affinities for the lectin. Scatchard analysis of the binding data indicates the presence of a class of high affinity sites which are saturated at about 0.25 μg/ml of Concanavalin A. The other, lower affinity binding sites are not saturated until 50–100 μg/ml Concanavalin A levels are achieved. At 4°C the K a for the high affinity sites varies between 1.5 – 5 × 10 9 M −1 depending on the method used to label the Concanavalin A. For the lower affinity sites K a varies between 1 – 4 × 10 6 M −1. The average number of high affinity sites per cell is 8 × 10 5 representing less than 1% of the total receptor sites for the lectin.