TIBS 18 - JULY 1993 example of mucins. Consequently, a func- tional role in maintenance of surface integrity, renewal and pathology of mucous epithelia seems likely. Acknowledgements We thank Dr R. A. Hughes for critically reading the manuscript. Our search for new P-domains has been supported by the 'Schilling-St[[tung'. References 1 Patthy, L. (1991) Curt. Opm Struct. BIol. 1, 351-361 2 Th=m,L. (1989) FEBS Lett. 250, 85-90 3 Tomasetto,C et al. (1990) EMBO J. 9,407-414 4 Jakowlew,S. B_ et al (1984) NucleJeAcids Res. 12, 2861-2878 5 Lefebvre,O. et al J. Cell Bfol. (m press) 6 Hauser, F. and Hoffmann, W (1991) J. Biol. Chem. 266, 21306-21309 7 Podolsky,D K. et aL (1993) J. Brol. Chem. 268, 6694-6702 8 HauseL F. et al. Prec. Nat/Acad. So. USA (in press) 9 Suemon, S., Lynch-Devaney, K and Podolsky, D K. (1991) Prec. Natl Acad. ,So. USA 88, 11017-11021 10 Chmery.R et al (1992) BJochem. J 285, 5-8 11 Rose, K et al. 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(1990) CancerCe/Is 2, 269-274 28 Rio, M-C. eta/ (1991) Gastroenterology 100, 375-379 29 Nunez, A-M, Berry, M, Imler, J-L and Charnbon, P. (1989) EMBO.I 8, 823-829 30 Jorgensen,K. D., Diamant, B., Jorgensen,K H. and Thlm, L (1982) Regul Peptldes 3, 231-243 31 Hoosem.N M, Thlm, L., Jorgensen,K H and Brattam, M G (1989) FEBSLett 247, 303-306 32 Chan, A. M-L eta/. (1991) Science 254, 1382-1385 33 Frandsen,E. K., Jorgensen,K H and Them, L (1986) ReguL PeptJdes 16, 291-297 34 Frandsen,E. K. (1988) Regu/. Pepbdes 20, 45-52 35 Chmery,R. eta/ (1993) Eur. J Biochem 212, 557-563 36 Bork, P. 1993) Prot So. 2, 669-670 Lateral communication by fast proton conduction: a model membrane study COMMUNICATION at the level of bio- logical membranes is mainly described as a trans phenomenon. In bioenergetic terms, energy transduction is considered to occur, mediated by transmembrane proton gradientsL But on each inter- [ace, the connection between pumps and sinks is considered to be either delocalized, i.e. occurring through the bulk phase, or localized, i.e. along the membrane' (Fig. I). The second case, the so called 'microlocalized' chemi- osmotic scheme, requires the existence of 'protonic networks '2 that would link pumps and sinks in small coupling units:L Recently, direct experimental evidence of the occurrence of such a lateral transfer has been demonstrated with model systems. Such a lateral transfer of information along the membrane may be a key process in biology. Proton transfer: a physlcochemical description All theoretical descriptions of proton conduction in biological systems are derived from the Bjerrum-Eigen- Onsager hypothesis 4 on the mechanism of proton conduction in ice. The basic J. Teissl6, B. Gabriel and M. Prats are at the Department of Glycoconjugates and Biomembranes, UPR8221 du CN S, 118 route de Narbonne,31062 Toulouse, France. © 1993, Elsevier 5c=ence Publishers, (UK) 0968-0004/93/$06.00 Lateral communication of information along biological membranes is thought to be a key process for many cellular activities, Support for this hypothesis comes from physicochemical experiments that show that an efficient fa- cilitated lateral proton conduction exists along lipid-water interfaces. The existence of a local two-dimensional hydrogen bond network between the lipid headgroups and their associated water molecules would explain this phenomenon. idea is linked to the presence of hydro- gen bonds between water molecules. Two processes are involved: (1) a pro- ton jumps from a 1130 ÷to a neighbouring H~.O molecule (hopping step); (2) proro- tational motion induces a small move- ment of the involved protons in one direction (Grotthus-type mechanism). A similar transfer has been described in biology. In the case of a proteinous proton channel, the proton movement was postulated to be due to the hydro- gen bond network linking the amino acids of the helix of a transmembra- neous protein 5. Two steps are again involved: (1) a hopping step where a proton jumps from one side-chain amino group, DH', to the neighbouring one, A; (2) a reorientahon step of the protonated acceptor AH ÷ through a flip- flop process to give a new donor DW. A more flexible network was pro- posed where the proton transfer along the proton channel was suggested to involve a mixed linear hydrogen bond system between amino acids and bound water molecules6. Such a composite network would allow (1) the adjust- ment of the distance between the donor and the acceptor of exchanged protons, and (2) a faster rotation of the groups than in a purely peptidic system. A 243