A new immunoglobulin marker.

In an examination of 16 human immunoglobulin lambda-light chains, one was found to have amino acid substitutions which have not previously been reported for the constant region of the lambda-chains. It involved in two positions: an arginine instead of lysine at position 130, and a leucine for glutamine at position 195 (Sh numbering (1) ). The structural variation is tentatively designated as "Is" marker.