Collect. Czech. Chem. Commun. 1979, 44, 1828-1834

Isoelectric focusing of insulin, 125I-insulin and the 125I-insulin-antibody complex

Asja Šiševaa, Jiřina Slaninováb, Tomislav Barthb, Stephan P. Ditzova and Luben M. Sirakova

a Diabetes Research Group, Endocrinological Institute, Medical Academy, Sofia, Bulgaria
b Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, 166 10 Prague 6, Czechoslovakia


Isoelectric focusing on polyacrylamide gel columns of three native crystalline commercial preparations of insulin and 125I-labelled insulin was carried out. All the compounds studied contained three components of different isoelectric points. The largest fraction, having pI 5.60 ± 0.05, was common to all preparations. The other two fractions were situated in the acid region of pH between pI 4.5 and 5.2. The presence of these fractions is explained by the contamination of crystalline insulins by proinsulin and by the formation of des-amido derivatives during the dissolving and storage of insulin samples, and, in case of labelled insulin, also by the presence of heavily iodinated insulin and contaminating components. The isoelectric focusing of the complex 125I-insulin-antibody showed a peak of radioactivity having pI 6.15 ± 0.05.