Trypsin protection assay. Wild-type, -10P, -10T, -10V, -10M, and –10L deletion variant AT proteins were translated by rabbit reticulocyte lysate in the presence of microsomes. The translation product was incubated with trypsin (t, see Materials and Methods) to digest product, which had not been translocated into the protected environment provided by the microsomal lumen. Relative protection from digestion of the 56-kD product is seen in translations of wild-type AT, -10V, and –10M variants. The 52-kD and 47-kD products from all translations were susceptible to trypsin digestion.