Figure 8. Detection of aquaporin-4 (AQP4)
in isolated ubiquitinated protein fractions. S5a is a protein subunit
of the proteasome that binds ubiquitinated proteins and can be used to
purify ubiquitinated proteins. Retinal ubiquitinated proteins were
purified on an S5a affinity column (Biomol Inc) before they were eluted
with SDS-sample buffer. Next, they were separated on SDS-PAGE then
subjected to western blotting using anti-AQP4 antibodies. As shown in
this figure, higher molecular weight forms of AQP4 were detected (87
and 100 kDa proteins). Lanes 1-3 are three different retinal
preparations from different rats.