On the possible permeation of water across the glucose transporter.

The possibility that the glucose transporter may serve as water channel is explored with the help of theoretical and experimental arguments. A model for a pore is drawn based on a hypothetical water channel structure, subject to the constraints that: molecules will bind to the channel wall in successive rings, forming a hollow sleeve; an integer number of molecules will exist in each ring; the pore radius will not be large enough to allow water molecules along its center, but will be large enough to allow glucose molecules across. The only configurations that meet these conditions exhibit either 5 or 6 water molecules abreast in each ring, with pore radii of 4.1 and 4.5 A, respectively. The kinetic characteristics of such pores are estimated and found to conform to available evidence.