Purification and assay of RhoPDE from HEK293 cells grown in the presence of ATR. (A) Absorption spectra of RhoPDE after purification (C8 antibody column) from HEK293 membranes. The figure compares the yield of RhoPDE from cells grown in the presence and absence of ATR: yellow, cells grown in the presence of ATR; and blue, cells grown in the absence of ATR. Membranes from cells grown in the absence of ATR were treated with retinal before detergent solubilization. No ATR was added to membranes from cells grown in the presence of ATR. (B) cGMP phosphodiesterase activity of RhoPDE in membranes isolated from cells grown in the presence of ATR. No additional ATR was added. The assay buffer for this reaction consisted of 50 mM HEPES (pH 6.5), 50 mM NaCl, 10 mM MgCl2, and 0.5 mM EDTA.