Western blot analysis of rat pk18 expressed in R. sphaeroides. The proteins (8.5 μg of protein per lane) were separated by SDS/Tricine electrophoresis, electroblotted onto nitrocellulose membrane, and probed with antibodies raised against rat pk18. Lane 1, urea-treated rat adrenal mitochondria; lanes 2–5, outer membrane preparations of TSPO1 (pAY13), 2.4.1(pAY13), TSPO1 (pRK415), and 2.4.1 (pRK415), respectively.