Elimination of size and charge heterogeneities of human leukocyte interferons by chemical cleavage

Abstract

Human leukocyte interferon (HuLeIF) preparations contain distinct molecular forms of interferon exhibiting significant heterogeneties in sizes when analyzed by electrophoresis in sodium dodecyl sulfate (NaDodSO(4))/polyacrylamide gels, migrating in two broad bands of activity with peaks at about 21,000 and 15,000 daltons. HuLeIFs exhibit extensive charge heterogeneities when analyzed by isoelectric focusing, resolving into several major peaks of approximately equal activity distributed from pH 5.7 to 7.0. When HuLeIF preparations are treated with 0.01 M sodium periodate buffer, pH 4.5, at 4 degrees , both the size and charge heterogeneities rapidly disappear: periodate-treated HuLeIF migrates as a single, narrow band at 15,000 daltons in NaDodSO(4)/polyacrylamide gels and focuses as a single, narrow band at pH 5.7. Quantitative considerations suggest that either the larger, heterogeneously charged HuLeIFs are converted to the smaller, size- and charge-homogeneous interferon by extensive chemical deglycosylation, or, alternatively, the smaller, 15,000 dalton, pH 5.7 interferon is much more stable to periodate treatment than are the other interferon forms. However, the activity of each of the variously charged forms of HuLeIF isolated from focusing gels exhibited the same stability as the pH 5.7 component; similarly, the activity of each of the size-forms of HuLeIF isolated from NaDodSO(4)/polyacrylamide gels exhibited the same stability as the 15,000-dalton interferon.