Figure 1. The proteolytic ¹⁸O labeling procedure uses a single tube.

*The photoreceptor OS membrane protein was prepared by precipitation with acetone to remove the lipids from the plasma and disc membranes, but depending on the nature of sample, this step may not be required. If acetone precipitation is not required, the excess of the TEP/IETH can be removed by speed-vac at 45°C. ** After every reconstitution step the sample was sonicated in a water bath for 10 sec. Formic acid can also be used instead of TFA. ***100 mM ammonium formate buffer (pH 6) can also be used. TEP (triethylphosphene), IETH (iodoethanol), ABC (ammonium bicarbonate), PFOA (perfluorooctanoic acid), ETAC (ethylacetate), EtOH (ethanol), TFA (trifluoroacetic acid), and NEM-AA (n-ethyl morpholine-acetic acid).