“…constant parts of immunoglobu lins) indicates that ASO activity may be associated with IgG, IgA, and even IgD; however, IgG, especial ly of the subclass G] and the K-type of the L chain, predominates. Since IgGik is the overwhelming frac tion in normal human immunoglobulins, a much greater number of myeloma proteins with ASO activi ty would have to be analyzed either to prove or to re fute an association between ASO activity and IgG]K. A restriction to a single immunoglobulin subclass and type has been shown for human anti-carbohydrate antibodies [22,35] and for cold agglutinins [24,27], An association between structure and specificity, however, is much more to be expected for the variable part of immunoglobulins than for the constant part, since the combining site resides in this section of the molecule. The L chain N-terminal amino acid se quences of the proteins O.I., L.F. and A.S. indicate that all three L chains fall into the same variable re gion subgroup, VkIII, while the H chains of both pro teins, O.I.…”