Water transport by the bacterial channel alpha-hemolysin

This study is an investigation of the ability of the bacterial channel alph a-hemolysin to facilitate water permeation across biological membranes. alp ha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at v arying concentrations, and water permeation was induced by mixing the ghost s with hypertonic sucrose solutions. The resulting volume decrease of the g hosts was followed by time-resolved optical absorption at pH 5, 6, and 7. T he average single-channel permeability coefficient of alpha-hemolysin for w ater ranged between 1.3 x 10(-12) cm/s and 1.5 x 10(-12) cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lowe r pi-I-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (E-a = 5. 4 kcal/mol), suggesting that the properties of water inside the alpha-hemol ysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculatio ns accurately predicted the rate of water flow through the channel. The lat ter finding also indicated that water permeation data can provide a good es timate of the pore size for large channels. (C) 1999 Elsevier Science B.V. All rights reserved.