Purification and Partial Amino Acid Sequence of Classical Anaphylatoxin from Pig Serum; Identification with Des-Arg-C5a

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Abstract
Complement was activated in hog serum and the biologically active peptide(s) derived from the 5th component of complement [C5] were purified. Treatment of the serum with yeast, without any precautions to inhibit serum arginine carboxypeptidase, allowed the recovery of only 1 active fraction, the classical anaphylatoxin; it was identified as des-Arg-C5a [secondary peptide fragment derived from fragment a of complement component 5]. When hog serum was activated with yeast in the presence of 1 M .epsilon.-aminohexanoic acid (inhibitor of arginine carboxypeptidase), 2 active C5-derived fractions were obtained, C5a and des-Arg-C5a. A partial amino acid sequence of the classical anaphylatoxin (19 N-terminal and 12 C-terminal amino acids) was elaborated. With 1 exception it is identical with hog C5a as far as that structure is known (12 N-, 3 C-terminal amino acids). The only difference is the C-terminal region; arginine, present in C5a, is absent from des-Arg-C5a which ends with Asn-Ile-Gln-Leu-Gly-OH. The finding that des-Arg-C5a, virtually free of any significant contamination with C5a, has considerable spasmogenic activity demonstrates that it is the classical anaphylatoxin. For spasmogenic activity, arginine as the C-terminal amino acid [apparently] is not absolutely essential.