Interferon: evidence for its glycoprotein nature

In an attempt to understand the structure of rabbit interferon, the possibility of carbohydrate being part of the molecule was tested. Interferon incubated with neuraminidase from Vibrio cholera is homogeneous in charge as revealed by isoelectric focusing. Treatment of "asialointerferon" with galactose oxidase (EC 1.1.3.9) from Dactylium dendroides and subsequent reduction with tritiated sodium borohydride yields labeled material with unimpaired antiviral activity. Enzymic incorporation of N-[(14)C]acetylneuraminic acid into tritiated asialointerferon restores the original charge heterogeneity. The newly generated sialointerferon contains both (3)H and (14)C activity. Asialointerferon is retained by an affinity column containing phytohemagglutinin from Phaseolus vulgaris and can be displaced from the adsorbent by a glycoprotein of known structure. It is concluded that rabbit interferon is a glycoprotein containing the terminal oligosaccharide sequence sialic acid --> galactose.