Abstract
Two forms of lambda Bence-Jones proteins, differing in a single amino acid in the invariant region, have been demonstrated. These polypeptide chains occur in 2 antigenic types, Oz (+) and Oz (-). Of 12 proteins studied, the seven Oz (+) proteins have lysine at position 190 and 5 Oz (-) proteins have arginine at the same position. This amino acid interchange resembles the interchange at position 191 of kappa polypeptide chains which is associated with the allotypic Inv factors.