Molecular size heterogeneity of human leukocyte interferon

Abstract

Molecular sieving of human leukocyte interferon revealed an apparent MW of 26,000. After denaturation by guanidine hydrochloride in the presence of a reducing agent and reactivation by extensive dialysis, a MW of only 21,000 was observed. The reactivated human leukocyte interferon (MW 21,000) gave a single peak of activity when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, confirming that a single MW species was generated by the denaturation and reactivation procedure. A partial unfolding of the molecule was evident when the interferon preparation was heated to 50.degree. C in the absence or presence of an unfolding agent and then sieved on Sephadex G-100 Superfine. The interferon molecule undergoes a proteolytic cleavage probably by a protease present in extracellular fluid. A peptide fragment apparently dissociates from the parent molecule when human leukocyte interferon is denatured in the presence of a reducing agent, resulting in a drop of 5000 in MW; interestingly, the resultant 21,000 MW form still retains its antiviral activity.