Evolution in the pancreatic chymotrypsinogen series: N-terminal sequence determinations and comparisons

Summary

The N-terminal amino acid sequences of chymotrypsinogens purified from the pancreas of three turtle species (Chelydra serpentina, Chrysemis picta andPseudemys elegans) have been determined, using automated Edman degradation. Homology has been established in the sequences of mammalian and reptilian chymo-trypsinogens. The first basic residue (and probable point of activating cleavage) was found, for reptilian chymotrypsinogens, to be at position 15, the same as in the cases of bovine and porcine chymotrypsinogens A and B. Although the comparative sequence information so far available in this series is limited, it suggests that a high rate of acceptance of replacement occurs in certain region of the chain: the variability observed can be interpreted in terms of the hypothesis of the selection of variants by the requirements for protein folding. The divergence of types of chymotrypsinogen is discussed.