Ia antigens contain two distinct forms of ? chain

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Abstract
Two new forms of β chain, β1 and β2, in I-A immunoprecipitates are described, which differ in their migration values in SDS-PAGE under nonreducing conditions, but which migrate identically in a reduced form. This behavior is very likely due to a different arrangement of intramolecular disulfide bonds which may influence mobility in SDS-PAGE. Peptide map analysis confirmed that β1 and β2, possess identical primary polypeptide structures. These two forms of β chain are also expressed on the cell surface and it is suggested that both associate with α chains. The structural differences in these complexes may lead to an increase in heterogeneity of la antigens which could be of importance for T-cell recognition.