Amino acid sequence of the active site of human serum cholinesterase from usual, atypical, and atypical-silent genotypes

Active-site tryptic peptides were isolated from three genetic types of human serum cholinesterase. The active-site peptide was identified by labeling the active-site serine with [³H] diisopropylfluorophosphate. Peptides were purified by high-performance liquid chromatography. Amino acid composition and sequence analysis showed that the peptide from the usual genotype contained 29 residues with the sequence Ser-Val-Thr-Leu-Phe-Gly-Glu-Ser-Ala-Gly-Ala-Ala-Ser-Val-Ser-Leu-His-Leu-Leu-Ser-Pro-Gly-Ser-His-Ser-Leu-Phe-Thr-Arg. The active-site serine was the eighth residue from the N- terminal. The peptide containing the active-site serine from the atypical genotype contained 22 residues with the sequence Ser-Val-Thr-Leu-Phe-Gly-Glu-Ser-Ala-Gly-Ala-Ala-Ser-Val-Ser-Leu-His-Leu-Leu-Ser-Pro-Gly. The peptide from the atypical-silent genotype contained eight residues with the sequence Gly-Glu-Ser-Ala-Gly-Ala-Ala-Ser. Thus, the sequences of the atypical and atypical-silent active-site peptides were identical to the corresponding portions of the usual peptide.