Two V-ATPase activity peaks were resolved by sucrose density
gradient centrifugation (10–50%, w/w) of the gill microsomal fractions
from crabs held in fresh water: a lighter fraction (I) at 24–32% sucrose
and a heavier fraction (II) at 39–44% sucrose (Fig. 4), demonstrating
that the enzyme occurs in membrane fractions of different densities.