Multiple charge isomers of human recombinant interleukin‐1β

Human interleukin-1 beta (rhuIL-1 beta), obtained by DNA recombinant technology, was radiolabelled. Its isoelectric properties were determined by various analytical techniques such as high-voltage ultrathin layer isoelectric focusing (IEF) and chromatofocusing. The rhuIL-1 beta molecule had a molecular mass of 18 kDa, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. When examined by IEF on a polyacrylamide gel of 1 mm thickness in the pH range of 3.5-9.5, it was resolved into two broad bands appearing in the pH range of 6.2-5.8 and 5.5-5.2. Each of the two bands was further resolved into multiple bands when electrofocused on (i) a thinner gel of 0.5 mm thickness and (ii) a narrower pH range of 5-8. Upon chromatofocusing in a liquid column, it was possible to isolate various charged components of rhuIL-1 beta. However, all these components reacted to the antiserum to rhuIL-1 beta and displayed a molecular mass of 18 kDa suggesting the charge heterogeneity of rhuIL-1 beta.