Description:
<jats:p>The signal segment of the secretory protein carp preproinsulin is shown to be bound by a protein receptor present in the rough endoplasmic reticulum membrane. The receptor does not bind the insertion segment of the integral membrane protein cytochrome <jats:italic>b</jats:italic><jats:sub>5</jats:sub>. On the other hand, the insertion sequence, in contrast to the signal sequence, is dissolved into the lipid bilayer of natural and artificial membranes. Hydrophobicity or length <jats:italic>per se</jats:italic> of the two types of peptides cannot be responsible for their different behaviour. We rather propose that the difference resides in their tertiary structure. Insertion peptides may form a compact structure with a diffuse hydrophobic surface, presumably by internal hydrogen bonding. Signal peptides would form hydrogen bonds with a membrane‐bound receptor protein, presumably by producing a β‐sheet structure, but their extended structure in aqueous solution would not allow them to dissolve into lipid bilayers.</jats:p>