Leukocyte interferon conjugated to beta-D-galactosidase for receptor studies: a preliminary report

In this report, we describe a simple procedure for labeling leukocyte interferon (IFN) with the enzyme beta-D-galactosidase (beta-gal), through a low-molecular-weight linking agent. The labeling procedure did not appear to alter the properties of the enzyme, the antiviral activity of the recombinant DNA-derived human clone A leukocyte IFN (rIFN alpha A), or the ability of the IFN to bind to Daudi cells. The binding of the putative IFN-enzyme complex to Daudi cells could be blocked by excess unlabeled IFN or by monoclonal antibody to IFN receptors. Our preliminary results indicate that enzyme labeling of IFN can result in a biologically active agent that has potential for use in the quantitation of circulating IFN and specific receptor proteins. In addition, this labeling procedure may be potentially useful with other immunomodulatory proteins.