1. JRU 206 Chimie Biologique, Agro Paris Tech, B.P. 1, F-78850 Thiverval Grignon, France; JRU 206 Chimie Biologique, INRA, B.P. 1, F-78850 Thiverval Grignon, France; Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague 6, 166 28 Czech Republic; and UR1268 Biopolymères Interactions Assemblages, Interfaces and Dispersed Systems Team, INRA, F-44300 Nantes, France