THE INSERTION BEHAVIOR OF WHEAT PUROINDOLINE-A INTO DIACYLGALACTOSYLGLYCEROL FILMS

In order to study the surface behaviour of puroindoline-a (PIN-a) in t he presence of lipid monolayers, protein solutions were injected benea th films of the polar wheat lipid diacylgalactosylglycerol (MGDG). It was found that injection of PIN-a into the sub-phase caused a surface pressure increase of monolayers consisting of MGDG. When PIN-a was inj ected beneath an MGDG film at an initial surface pressure (pi(initial) ) between 9 and 15 mN/m, a relatively fast increase in the surface pre ssure to 17 +/- 2 mN/m was observed (the maximum surface pressure that could be reached by the protein alone). Then a much more gradual incr ease in pi was observed. At pi(initial) values exceeding 35 mN/ m, inj ection of PIN-a resulted in a gradual increase in pi to 49 +/- 1 mN/m, which is equal to the collapse pressure of a pure MGDG monolayer. A g radual increase in the surface pressure was observed after injection o f PIN-a beneath an MGDG monolayer with pi(initial) values between 15 a nd 35 mN/m, but the final value was lower than the collapse pressure o f pure MGDG. Injection of peptide-a (a peptide comprising the tryptoph an-rich domain of PIN-a) beneath MGDG monolayers also led to a conside rable increase in surface pressure. The data are interpreted as insert ion of PIN-a or peptide-a into the MGDG films. Tn contrast to this, li pid-transfer protein did not show this behaviour under the same condit ions. The present data suggest that PIN-a may be present at the pas-ce ll surface in dough. However, although the elasticity of mixed PIN-a/M GDG films somewhat decreased owing to protein insertion, the resulting monolayer would still retard disproportionation. (C) 1998 Academic Pr ess.