Presence of insulin binding sites on viral particles.

Using a standard radio-receptor assay, we have demonstrated that [125I]insulin can bind specifically to each of two types of purified enveloped viruses, influenza A virus and Rous sarcoma virus. A non-enveloped icosahedral virus (echovirus 11) and herpes simplex virus type 2, which acquires its envelope from the nuclear membrane of the cell, did not possess insulin receptor activity. Displacement of specifically bound radiolabelled insulin from the viral surface was achieved by addition of an excess of unlabelled insulin but not by addition of another unrelated protein, cytochrome C. We conclude that certain types of enveloped viruses may acquire insulin binding sites from the plasma membrane of their host cell.