The titration curves of chymotrypsinogen and α-chymotrypsin in water, 20% formol, and 8 M urea have been determined. The curves for chymotrypsinogen are consistent with its reported amino acid content. The curves for α-chymotrypsin, however, indicate an excess of one group over that which would be expected from the amino acid content. The group is cationic, titrates in the extreme alkaline region, and may be tentatively identified as a guanidino residue. No evidence for abnormal carboxyl groups in chymotrypsinogen or α-chymotrypsin were found.
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