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pH-dependent polymerization of a human leukocyte interferon produced by recombinant deoxyribonucleic acid technology.

The pH-dependent polymerization of human leukocyte interferon A produced by recombinant DNA technology was investigated by potentiometric hydrogen ion titration and sedimentation velocity analytical ultracentrifugation. The titration curve is completely reversible from pH 6.2 to 2.5. Analysis of the side-chain carboxyl residues by using the Linderstrøm-Lang equation yields a linear plot from pH 5.2 to 3.5. The resulting pKint and W values are 4.66 +/- 0.06 and 0.036 +/- 0.004, respectively. The titration curve from pH approximately 9.6 to 7 is also reversible. However, the reverse titration from pH 7 to 6 results in a time-dependent variation of pH. Sedimentation velocity analysis yields an increase in the corrected sedimentation coefficient, S20,w, from 2.0 to 4.0 S over a pH range of 2.5-9 at 0.38-0.25 mg/mL total protein concentration. The concentration dependence of the sedimentation coefficient at pH 7.0 over the range of 0.05-6.0 mg/mL results in a positive slope which is typical for self-aggregating systems. This aggregation phenomenon is discussed in terms of its ramifications for interferon therapy.