Concanavalin a binding as a tool in determining the sidedness of membrane vesicles from maize coleoptiles

Abstract

Plasma membrane(PM)-and endoplasmic reticulum(ER)-rich fractions from etiolated maize coleoptiles were assayed for their ability to bind concanavalin A (Con A). Evidence is presented for lectin binding sites in both fractions, proving the presence of available mannosyl and /or glucosyl residues on the membrane surface of vesicles. Results from quantitative binding studies using [ 3H] Con A showed that Con A binding is specific, of high affinity and saturable. Compared to ER vesicles, PM vesicles bound three times as much Con A. Con A binding by both fractions was also assessed after disruption of the vesicle membrane by Triton X-100 or low pH. While a dramatic increase in binding capacity of Con A to ER vesicles was achieved after treatment with low concentrations of detergent or at pH 5.0, the level of Con A binding to PM vesicles was not altered, indicating that these treatments did not expose additional lectin binding sites. Results are discussed in relation to the sidedness of PM and ER vesicles.