Rat-Proinsulin C-Peptides.

The amino acid sequences of two rat C-peptides corresponding to two rat proinsulins have been elucidated. Both C-peptides have 31 amino acids. There are differences in two positions, namely, in position 8 where rat-I has a proline and rat-II an alanine residue, and in position 17 where rat-I has a glutamic acid, rat-II a glycine residue. The additional acidic residue in rat-I C-peptide is counteracted by the additional basic residue in the insulin moiety of rat-I proinsulin (lysine B 29), which provides the two proinsulins with the same net charge at neutral pH. The amino acid sequences are: Glu-Val-Glu-Asp-Pro-Gln-Val-I:Pro/II:Ala -Gln-Leu-Glu-Leu-Gly-Gly-Gly-Pro-I: Glu:/II: Gly-Ala-Asp-Gly- Leu-Gln-Thr-Leu-Ala-Leu-Glu-Val-Ala-Arg-Gln. The rat C-peptides contain threonine and arginine, neither of which is present in the C-peptides of man, pig and ox. A comparison of the 5 sequences shows only 10 identical positions out of 31. [ABSTRACT FROM AUTHOR]