N-terminal amino-acid sequence of African lungfish immunoglobulin light chains.

The sequence of the N-terminal ten amino acids of the unblocked light chains derived from the low molecular weight immunoglobulin of a dipnoid fish, the African lungfish (Protopterus aethiopicus), has been determined. A degree of sequence heterogeneity as extensive as that displayed by pooled mammalian light chains was encountered. The major N-terminal sequence of the amino acids of light chains from lungfish immunoglobins can be made homologous with that of various Elasmobranchean, Chondrostean, Avian, and Mammalian species if an internal deletion of two base triplets in the gene coding for light chains from lungfish immunoglobulins is assumed. The existence of a deletion and/or insertion mechanism may have profound biological significance, since it would be ideal for the introduction of variability into immunoglobulin chains without sacrificing certain integral features of the antibody molecule.