IPP2 has been shown to be as sensitive to fluoride as IPP1 in vitro; therefore, our results probably reflect the fact that HF, the actual molecule that permeates membranes, is mostly dissociated into F- ad H+ in yeast cytosol, which is normally maintained at pH values of 7.2–7.4 [47]. This evidence concerns the gene PPP1R2 and hydrops fetalis.