Lateral diffusion of macromolecules in monolayers at the air/water interface

Abstract

We report a lateral diffusion study of a surface active protein, bacterial lipase from pseudomonas fluorescens, and a vinyl polymer, poly(t-butyl methacrylate) on the air/water interface by the technique of fluorescence recovery after photobleaching. For the validation of our technique and the calibration of the instrument, we relied on a phospholipid system that Peters and Beck used earlier, and found that our results were in accord with theirs within 20% in absolute magnitude. For both the phospholipid and lipase, we analyzed the lateral diffusion data in terms of the free area model of Sackmann and Träuble. We conclude that the results of lipase could be interpreted by invoking a conformational change induced by lateral compression in the monolayer state, and those of the polymer by postulating the quenching of the diffusion process in the dilute region when its surface concentration enters into the semidilute region.