Solubilization of soybean membrane binding sites for fungal β-glucans that elicit phytoalexin accumulation

Soybean membranes contain high-affinity binding sites for fungal β-glucans. These sites may play a role in the recognition by soybean tissues of fungal phytoalexin elicitors. We have solubilized β-glucan-binding activity from microsomal membranes using two C₁₂,-alkyl zwitterionic detergents, Zwittergent 3-12 (ZW 3-12) and the lysolecithin analog l-dodecyl-2-deoxy-phosphorylcholine (ES12H). The solubilized binding sites displayed identical affinity for β-glucans as that found in membranes (K_d= 11-34 nM). Detergent-protein micelles with glucan binding activity eluted with approximate M_r values of 300000 in ZW 3-12 and 380000 in ES12H in gel permeation chromatography. Maximal binding activity eluted from a chromatofocusing column in the pH range between 6.2 and 6.6 with both ES12H and ZW 3-12, suggesting an apparent pIclose to neutral.