Some aquaporins can transport NH 3 and CO 2 . Glycerol facilitators function as solute nonspecific channels, and transport glycerol, dihydroxyacetone, propanediol, urea and other small neutral molecules in physiologically important processes. Several reports of MIP family proteins transporting ions may or may not be physiologically significant. The physiological functions of many MIP family proteins are unknown. The two halves of the proteins are therefore of opposite orientation in the membrane.
Glycerol molecules line up in single file within the amphipathic channel.
Thus each half of the protein forms 3.5 TMSs surrounding the channel. The structure explains why GlpF is selectively permeable to straight chain carbohydrates, and why water and ions are excluded. Phylogenetic characterization of the MIP family of transmembrane channel proteins. Molecular design of aquaporin-1 water channel as revealed by electro crystallography. Regulation of the Escherichia coli water channel gene aqpZ .