Cratylia mollis lectin at the air-aqueous solution interface:: adsorption and lectin-lipid interactions

The interfacial behaviour of Cratylia mollis (Cra) at the air/water interface and its penetrant ability into spread phospholipid monolayers (Lipoid E80 and Epicuron 200) has been monitored by surface tension measurements. The first-order rate constants defining adsorption and rearrangement obtained from surface tension kinetics data reveal that Cra is a rather stable protein which exhibits characteristic protein adsorption patterns in which the breaking points separating diffusion-penetration and rearrangement profiles could have been easily distinguished. The penetration of Cra into Lipoid E80 and Epicuron 200 phospholipid monolayers has been inferred in terms of penetration pressure increments (Delta Pi) versus time relationships. The data clearly showed that penetrant ability of the lectin was, to a large extent, dependent on monolayer compressibilities. Thus, for Lipoid E80, which contained a rather high percentage of phosphatidylethanolamine (DPPE) in the mixture with phosphatidylcholine (DPPC), penetration of Cra at the high monolayer compression (20 mN m(-1)) was lower than that observed for Epicuron 200, which did not contain DPPE. Indeed, in the middle of the Pi-A isotherm, DPPE was markedly less compressible than DPPC. However, at the low monolayer surface coverage (3 mN m(-1)), the rates of Cra penetration into both Lipoid E80 and Epicuron 200, although much higher for the latter at the beginning of adsorption, yielded similar limiting values of Delta Pi. This has been attributed to the occurrence of a hydrophobic interaction between the lectin and hydrophobic phospholipid chains that have the same length for both Lipoid E80 and Epicuron 200. (C) 2000 Elsevier Science B.V. All rights reserved.