Ad. Pemberton et al., SHEEP MAST-CELL PROTEINASE-1 - CHARACTERIZATION AS A MEMBER OF A NEW CLASS OF DUAL-SPECIFIC RUMINANT CHYMASES, Biochemical journal, 321, 1997, pp. 665-670
Sheep mast cell proteinase 1 (SMCP-1), which is abundantly expressed i
n gastrointestinal but not skin mast cells, was isolated and its subst
rate specificity was investigated. Peptide substrates, including angio
tensin I, substance P, bradykinin and oxidized insulin B chain were hy
drolysed at P1 Phe, Leu or Tyr residues, conforming to the known chymo
trypsin-like properties of the enzyme. However, SMCP-1 was found to hy
drolyse some chromogenic substrates with P1 Lys and Arg residues. The
enzyme also demonstrated trypsin-like activity against protein substra
tes, cleaving BSA at Lys(114)-Leu(115), Lys(238)-Val(239), Lys(260)- T
yr(261) and Lys(376)-His(377). Bovine fibrinogen beta-chain was cleave
d at Lys(28)-Lys(29). To ensure homogeneity of the enzyme, the ratio o
f chymotrypsin-like to trypsin-like activity was observed; it was foun
d to be constant during purification and between different preparation
s of SMCP-1. Treatment of SMCP-1 with a range of inhibitors decreased
chymotrypsin-like and trypsin-like activities by similar extents, supp
orting the assertion that both activities are the property of a single
enzyme. In terms of activity, and by N-terminal amino acid sequencing
, SMCP-1 strongly resembles the similarly dual-specific bovine duodena
l proteinase, duodenase. It is proposed that SMCP-1 and duodenase repr
esent a new class of ruminant chymases with unusual dual specificities
.