The microheterogeneity of desialylated alpha 1-antichymotrypsin: the occurrence of two amino-terminal isoforms, one lacking a His-Pro dipeptide.
ACT (alpha 1-antichymotrypsin), a serine antiproteinase with specificity against neutrophil cathepsin G, is homologous with alpha 1-antitrypsin, plasminogen activator inhibitor and angiotensinogen, all with known amino-terminal microheterogeneity. Here we report that the two predominant isoforms of desialylated ACT obtained on isoelectric focusing correspond to a microheterogeneity at the amino terminus of ACT: one isoform (His-Pro-Asn-Ser-Pro-) and a two residues shorter isoform (Asn-Ser-Pro-). The relative occurrence of the two isoforms was comparable both in normal plasma, acute-phase plasma and plasma from subjects with heterozygous familial ACT deficiency. When desialylated ACT, isolated by affinity chromatography from ACT-deficient, normal or acute-phase plasma, was compared with regard to mass and charge microheterogeneity, we found no significant differences in either respect. Nor was the isoform pattern of desialylated plasma from patients with rheumatoid arthritis different. Although the occurrence of heterozygous familial ACT deficiency implies genotypic variation, isolated ACT from patients with the trait was not found to exhibit any phenotypic variation detectable by standard electrophoretic methods.
Lindmark
B
B
Department of Medicine, University of Lund, Malmö General Hospital, Sweden.
Lilja
H
H
Alm
R
R
Eriksson
S
S
D000595:Amino Acid Sequence; D002846:Chromatography, Affinity; D004151:Dipeptides; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D000514:alpha 1-Antichymotrypsin / Q000097:blood* / Q000172:deficiency
D004151:Dipeptides; D000514:alpha 1-Antichymotrypsin; C035699:histidylproline