The sharp pH threshold observed suggests that there may be other cellular mechanisms able to partially compensate for loss of V-ATPase activity under certain pH conditions. Thus, V-ATPase plays a primary role in intracellular pH and ionic regulation in yeast. A high degree of sequence similarity among Vma6p homologues from various species suggests that this subunit has a conserved role in V-ATPase function. The wide phylogenetic distribution and presence of several highly conserved domains within all polypeptides examined support the hypothesis that Vma6p has a conserved role in V-ATPase function and assembly. Since yeast Vma6p is required both for stable assembly of the V0 sector and V1 attachment we have hypothesized that it may play a role in regulation of V-ATPase assembly.
Much information is available about the function of vacuoles in higher plant cells.
In particular, the ion transport activity of tonoplast membranes has been well characterized using combined biochemical and electrophysiological approaches. While in vivo studies of yeast V-ATPase assembly and function have yielded much information, isolated vacuolar membranes are relatively labile, and thus somewhat more difficult to work with in vitro. In contrast, higher plant tonoplast membranes highly enriched in V-ATPase activity may be easily isolated in large quantities and stored frozen. Thus, plant systems seem to be well suited for examining V-ATPase regulation at biochemical and cellular levels. As a visiting scientist in the lab of Dr. Don Briskin in 1996, I began studying V-ATPase isolated from red beet storage tissue.