Interchain and Intrachain Disulfide Bridges of a Human Immunoglobulin M: Detection of a Unique Fragment

Studies of the amino acid sequences around half-cystine residues in an immunoglobulin M have revealed an unexpectedly high number. At least 14 different sequences were found in the μ chain (V_HIII subclass). Four of these were involved in interchain disulfide bridges and at least 10 in intrachain bridges. Five came from the κ chain (κ_III subclass, Inv b). Several others, although having a high degree of homology, were not identical with those of either the μ or κ chains. These results support the concept of an additional fragment in γM molecules, although its function and localization remain to be determined.