The amino acid sequences of the amino-terminal of the two different polypeptide chains of the human decidua-associated protein hDP200, with apparent molecular masses of 55 and 25 kDa, were determined. The amino-terminal sequence of the 55 kDa chain revealed that it is an immunoglobulin heavy chain, of the VH\p=n-\III subgroup and the amino-terminal sequence of the 25 kDa chain showed that it is a human kappa V\p=n-\III light chain. The sequence data indicate that hDP200 is an immunoglobulin.

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... ability of the hDP200 molecules to form high molecular weight complexes with immunoglobulins of other classes suggest that hDP200 is a rheumatoid factor.