Accessory subunits of the V-ATPases are believed to be non-essential for the function of the proton pump, but act to modify activity. They are not found in unicellular organisms. (Adapted from FBrf0220613).
Notes on Group
The VhaM8.9 gene product also functions as a receptor for prorenin and renin in mammals (it is also known as the (pro)renin receptor (PRR)). The renin/prorenin system is absent in Drosophila (FBrf0223789).