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Amino Acid Sequences of Free and Blocked N-Termini of Leopard Shark Immunoglobulins¹

From the Department of Microbiology, University of California, San Francisco, San Francisco, California 94122

Abstract

Peptides with N-terminal pyrrolidonecarboxylic acid (PCA) were isolated from the heavy and light chains of leopard shark immunoglobulins. The complete amino acid sequences of three such peptides from the H chains of both 19S and 7S proteins, and the partial sequence of a peptide from the L chains, were determined. The sequences bore little homology to the variable (V) region sequence of human H chains. Leopard shark H and L chains were also subjected to 10 cycles of automatic Edman degradation. The sequences of the H chains of the 19S and 7S proteins were identical, as were those of the L chains. The yields obtained indicate that at least 40% of the H chains and 25% of the L chains had free N-terminal residues. The H chain sequences showed substantial homology with human H chains, but the degree of homology with human V_H, V_K, V and shark V_L was approximately the same. The L chain sequence exhibited equal homology with human V_K and V, but was less closely related to human V_H. These results show that the leopard shark, like mammals, has both blocked and free N-terminal sequences in its immunoglobulin H and L chains. This indicates that genetic divergence of V-region subclasses was an early evolutionary event.

Footnotes

¹ This investigation was supported by United States Public Health Service Grants AI 05664 and AI 00299.

² G. G. B. K. is the recipient of United States Public Health Service Research Fellowship Grant 5-F2-AI-35,773-3, and Bank of American Giannini Foundation Research Fellowship.

³ Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy, University of California, San Francisco.