Fig. 6.

Assaying for protein membrane integration. Schematic representation of the protein band patterns expected for transmembrane, and secretory proteins after incubating the microsomes at neutral and alkaline pH. At neutral as well as alkaline pH, membrane-integrated connexin polypeptides remained associated with the microsomal membranes and were detected in the pellet fraction (p) (lanes 2 and 4). Full-length, not membrane integrated connexins were detected in the soluble supernatant fraction (s) (lanes 1 and 3). A similar result was obtained with the glycosylated, transmembrane control protein acetylcholine receptor subunit α7 (AchRα7) (⩼lanes 5–8), while the secretory control proteins prolactin and yeast α-factor were extracted from the microsomal membranes at alkaline pH and were detected in the supernatant fractions (lanes 10, 14, and 12, 16).