Proteinase isoinhibitors from bovine spleen: primary structure of an intermediate in the processing of the precursor.
The complete amino acid sequence of the proteinase inhibitor III from bovine spleen is reported. It consists of 62 amino acid residues and is identical to that of spleen inhibitor II (an isoinhibitor of the bovine pancreatic trypsin inhibitor, which shares with the latter 89% of sequence identity), except for four extra residues at the C-terminal side. Inhibitor III appears to be an intermediate in the processing of the putative 100-residue primary expression product, which leads to the mature inhibitor II. These results and those previously obtained for another intermediate, isoinhibitor I, are indicative of the following order for the last steps of the precursor processing inhibitor I----inhibitor III----inhibitor II. The mature protein and the two intermediates isolated have a very similar antiproteolytic activity. However, their in vivo target enzyme(s) are not yet known, as also the target enzyme of the bovine pancreatic trypsin inhibitor is not known. Thus, the available data would indicate that either the three isoinhibitors have a distinct functional role, by inhibiting different target enzymes, or inhibitors I and III are obligatory intermediates for directing the final targeting of the mature, functionally relevant inhibitor II.
Barra
D
D
Department of Biochemical Sciences, University of Rome La Sapienza, Italy.
Fioretti
E
E
Angeletti
M
M
Maras
B
B
Bossa
F
F
Ascoli
F
F
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D007611:Aprotinin / Q000031:analogs & derivatives*; D002417:Cattle; D008969:Molecular Sequence Data; D011480:Protease Inhibitors / Q000737:chemistry / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D012689:Sequence Homology, Nucleic Acid; D013154:Spleen / Q000378:metabolism*; D014361:Trypsin Inhibitors / Q000737:chemistry / Q000378:metabolism*
D000596:Amino Acids; D011480:Protease Inhibitors; D011498:Protein Precursors; D014361:Trypsin Inhibitors; C062659:spleen protease inhibitor II; D007611:Aprotinin