Journal of Structural Biology 149 (2005) 158–169 www.elsevier.com/locate/yjsbi 1047-8477/$ - see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jsb.2004.11.003 Many length scales surface fractality in monomolecular Wlms of whole myelin lipids and proteins Rafael G. Oliveira a,b , Motomu Tanaka b , Bruno Maggio a,¤ a Departamento de Química Biológica-CIQUIBIC, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, 5000 Córdoba, Argentina b Lehrstuhl für Biophysik E22, Physik Department, Technische Universität München, 85747, Garching, Germany Received 10 March 2004, and in revised form 9 November 2004 Available online 8 December 2004 Abstract Monomolecular Wlms prepared with all the lipid and protein components of myelin were spread at the air/aqueous buVer interface from isolated bovine spinal cord myelin fully dissolved in chloroform:methanol (2:1) or by surface free energy shock of myelin mem- brane microvesicles. These monolayers show indistinguishable surface behavior, with similar compositional phase coexistence through all the compression isotherm on several subphase conditions. The domains were observed through epiXuorescence and Brewster angle microscopy on the air/water interface and on Langmuir–Blodgett Wlms. Their thickness was measured ellipsometri- cally. Under molecular packing conditions resembling those found in the natural membrane, the morphology and size of the domains are highly self-similar, displaying no characteristic length scale. These properties are the hallmark of fractal objects. The fractality extends at least three orders of magnitudes, from the micrometer to the millimeter range, the fractal dimension being about 1.7. A possible implication of fractality in membrane structure and/or function is demonstrated through the high Xuctuation of the propagation of signals through constrained diVusion in corrals formed by domains in the plane of the monolayer, which restricts the diVusion of a Xuorescent probe over many length scale domains.  2004 Elsevier Inc. All rights reserved. Keywords: Monolayers; Myelin; EpiXuorescence microscopy; Langmuir–Blodgett Wlms; Lipid–protein domains; Fractals 1. Introduction There is an increasing body of evidence regarding the lateral coexistence of phase domains formed by diVerent components in biological membranes. However, the molecular base and underlying physico-chemical forces leading to such microheterogeneity remain to be known (Maggio et al., 2004) and this impairs possibilities for prediction of the typical size of lipid domains in bio- membranes. In monolayers at the air/water interface the equilibrium lipid domain radii can be readily measured; moreover, they can be calculated and roughly predicted from the relation between the domain line tension and the diVerence in the perpendicular surface dipole moment density between coexisting domains (Härtel et al., 2004; McConnell, 1991). Nevertheless, although the last variable is relatively straightforward to measure, the Wrst one is rather complicated (Benvegnu and McConnell, 1992; Würlitzer et al., 2000). There is discrepancy about the typical size of domains in membrane systems (Edidin, 2001; Yuan et al., 2002), ranging from some nanometers as calculated for phospholipid phase transitions and mixed systems with cholesterol (Mouritsen, 1990), to the order of microme- ters in giant unilamellar vesicles (Dietrich et al., 2001) and can be even larger in unrestricted size monolayers formed by complex natural membrane surfaces (Oliveira and Maggio, 2002). Lipid domain sizes (in mixed mono- layer of dioleoylphosphatidyl choline, sphingomyelin GM1 and cholesterol, ceramide, and sphingomyelin) of * Corresponding author. Fax: +54 351 4334074. E-mail address: bmaggio@dqb.fcq.unc.edu.ar (B. Maggio).