Desorption of spread monolayers of [ 14C] methylated and cold BSA from the air—aqueous interface

Abstract

Compression—expansion cycles on spread monolayers of BSA and [ 14C] methylated BSA at the air/phosphate buffer interface at 20°C showed that irreversible losses in area occurred after films were held at surface pressures greater than 18 mN m −1, although the compressibility was unchanged. The rates of desorption of BSA and of a 2:1 mixture with radiolabelled BSA were similar at ∏= 21, 24 and 30 mN m −1, and increased with increasing surface pressure. The surface concentration of protein obtained after successive cycling, from the activity of the labelled monolayer transferred onto plates by the Langmuir—Blodgett technique, was constant within experimental error, indicating that area losses were caused by desorption. Activity measurements of aliquots of the substrate confirmed desorption into the subphase. The calculated mass of protein in the subphase was greater than calculated for the decrease in area at 10 mN m −1; it was concluded that at least 3–5% of protein was lost to the subphase although an accepted spreading technique was used.