The existence of infinite periodic lipid bilayer structures in biological systems was first demonstrated in cell membrane assemblies. Such periodicity is only possible in symmetric bilayers, and
their occurrence is discussed here in relation to
the asymmetry of cell membranes
in vivo. A periodic membrane conformation in
the prolamellar body of plants corresponds to a dormant state without photosyn
thesis. A similar reversible formation of a dormant state has also been observed in
the mitochondria of
the amoeba
Chaos. In
these cases
the energy production has become insufficient to maintain
the membrane asymmetry. Formation of membranes that are symmetric over
the bilayer is proposed to be a principal mechanism behind formation of cubic membrane systems.
Another type of bicontinuous minimal surface structure is considered to form the alveolar lining of mammals at normal breathing conditions. The CLP surface corresponds to such a tetragonal surface phase. It is also a symmetric bilayer and in a state of zero energy expenditure. Structural alternatives of the bilayer conformation in this latter system are also discussed here.