Zur Strukturregel der Antikörper. Die Primärstruktur eines monoklonalen IgG1-Immunglobulins (Myelomprotein Nie), III. Die chymotryptischen Peptide der H-Kette, Anordnung der tryptischen Peptide und Diskussion der vollständigen Primärstruktur

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Abstract
The complete primary structure of the H-chain of immunoglobulin Nie (IgG1, Gm1+, 17+) [from human myeloma] is established by overlapping tryptic fragments with chymotryptic peptides. The .gamma.1-chain Nie comprises 448 amino acid residues. When the protein is compared with other H-chains, the switch from the variable to the constant part occurs at position 119/120. Based on the amino acid sequence of the variable part, protein Nie belongs to subgroup III of the H-chains. It was the 1st protein of this subgroup to be sequenced. Protein Nie is the 1st completely determined chain with the genetic factors Gm1+, 17+. These factors are inherited codominantly and are localized on the constant part of the .gamma.1-chain. By comparison with protein Eu, which is Gm1-, 4+ and therefore an allele of Nie, these serologically defined factors are correlated with Eu. Besides the amino acid exchanges caused by the Gm-factors, a series of differences to the constant part of the protein Eu were differentiated. These differences include 6 amide positions and the sequence from residues 387-391. Using the structure of IgG1 Nie as an example, some rules for the evolution of immunoglobulin sequences were described. In particular the elongation-rule and the disulfide-rule are discussed. While chain-elongation of the H-chains can simply be explained by repeated gene duplications of a basic unit containing about 110 amino acids, the location of disulfide bonds is determined partly by gene duplication, which implies multiplication of evolutionary old cysteine residues and partly by the relatively recent acquisition of new cysteine in approximate sites. Most evident is the origin of the hinge-region by partial gene duplication of the C-terminal residues of the first homology region.