The N-terminal sequence of the heavy chain of rabbit immunoglobulin IgG.

The absence of an N-terminal amino acid with a free alpha-amino group from the heavy chain of rabbit immunoglobulin IgG has been confirmed and no evidence could be found of a blocking formyl, acetyl or propionyl group. The N-terminal amino acid appears to be pyrrolid-2-one-5-carboxylic acid (PCA) in all molecules. A mixed amino acid sequence follows in the approximate proportions: PCA-Ser-Val-Glu-Glu-Ser-Gly-Gly-Arg, 50%; PCA-Ser-Leu-Glu, 20%; PCA-Glu(NH(2)), 20%. The heavy chains of a purified antibody, namely anti-(human serum albumin), and of immunoglobulin IgG from a rabbit homozygous at the allotypic loci both showed a similar mixed N-terminal sequence.