RTA binds to ER microsomal membranes. 0.25 μm
(A) 2.5 μm (B) RTA259-NBD were
incubated in buffer H for 30 min on ice (0 °C) or at 26 °C with either
microsomal membranes (+KRM; 20-40 eq) or an equal amount of buffer
without microsomes (-KRM). Free RTA259-NBD was then
separated from KRM-bound RTA259-NBD either by sedimentation
(A) or by gel filtration chromatography (B). A,
following sedimentation, the supernatant (s) and the microsomal
pellet (p) were analyzed by SDS-PAGE. NBD-labeled proteins were
visualized using a fluorescence imager. B, following mixing, free and
KRM-bound RTA259-NBD were separated by gel filtration
chromatography in buffer H at 4 °C using a Sepharose CL-2B column (8
× 0.5-cm inner diameter). Each fraction was scanned for the presence of
RTA259-NBD (•; λex = 468 nm;
λem = 530 nm) and KRMs (▾; λex = 405
nm; λem = 420 nm). As controls, only RTA259-NBD
(○) or only KRMs (▿) were run and analyzed separately.