Functional analysis of heterologously expressed TaTIP2;2 by means of stopped-flow spectrometric studies provide evidence for water and ammonia conductivity. A series of experiments under increasing pH indicate that the gaseous NH(3), rather than the ammonium ion NH(4)(+) was transported. Results from inhibitor studies strongly suggest that NH(3) is not transported in file with water, but through a separate pathway, which could be supplied by the 5th central pore in a tetramer conformation.