[Identification of membrane proteins of sarcoplasmic reticulum binding 2,4,6-trinitrobenzene sulfonate]

Sarcoplasmic reticulum was treated with 2,4,6-trinitrobenzene sulfonate (TNBS), which binds covalently only with surface amino groups. After solubilization of the membranes and gel-filtration of the SR protein on the Sephadex G-100, the label was discovered in the protein fraction 100-80 and 70-60 kDa. The amino groups of proteins with molecular weight 50-20 kDa are inaccessible for the 2,4,6-TNBS. Incorporation of the latter into proteins increases in presence of KCl.