IMMUNOGLOBULIN DIVERSITY IN THE PHYLOGENETICALLY PRIMITIVE SHARK, HETERODONTUS FRANCISCI: I. SUGGESTED LACK OF STRUCTURAL VARIATION BETWEEN LIGHT CHAINS ISOLATED FROM DIFFERENT ANIMALS

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Abstract
A two-step procedure employing gel filtration and anion exchange chromatography has been utilized to isolate LMW immunoglobulin from the horned shark, Heterodontus francisci. Light chains obtained by complete reduction and alkylation of the parent protein have been compared by several analytical techniques. Amino acid composition data implies a limited degree of variation in the light chains isolated from individual animals. Polyacrylamide gel electrophoresis of the CNBr digests of the light chains reveal indistinguishable banding profiles of the major peptides. Isoelectric focusing indicates limited heterogeneity in the light chain spectrotype and identity in the pI of the majority of bands detectable by staining. The suggested degree of structural similarity in the light chains of this phylogenetically primitive shark is discussed in terms of the evolutionary position of the species and current theories concerning the origins of structural diversity in immunoglobulins.