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J. Biol. Chem., Vol. 262, Issue 20, 9615-9620, Jul, 1987
Enzymes that process somatostatin precursors. A novel endoprotease that cleaves before the arginine-lysine doublet is involved in somatostatin- 28 convertase activity of rat brain cortex
P Gluschankof, S Gomez, A Morel and P Cohen
The selective processing activity which generates both the NH2- and
COOH-terminal fragments of the octacosapeptide somatostatin-28 (S-28) was
investigated. Separation into two distinct proteolytic activities was
achieved by ion-exchange chromatography. An endoprotease cleaving either
the substrate Pro-Arg-Glu-Arg-Lys-Ala-Gly-Ala-Lys-Asn-Tyr-NH2, i.e.
[Ala17,Tyr20]S-28-(10-20)-NH2 (peptide I), or the octacosapeptide
somatostatin-28, on the NH2 side of the Arg-Lys doublet was separated from
an aminopeptidase B-like activity. Whereas the endoprotease cleaves a
single peptide bond, between Glu12 and Arg13 of S-28, the aminopeptidase
B-like enzyme removes both Arg13 and Lys14 stepwise from the NH2 terminus
of the corresponding COOH-terminal fragment. This endoprotease activity
peaks around pH 8.5, whereas the optimal aminopeptidase B-like activity is
in the pH range 6.2-8.5. Combination of both enzymes resulted in the
recovery of the overall S-28 convertase activity with an optimal pH at 7.
In addition, this endoprotease appears to be very sensitive to divalent
cations since it is strongly inhibited by chelating agents. The use of
selectively modified undecapeptides derived from the reference substrate
peptide I by a single modification of the amino acids Glu12, Arg13, and
Lys14 at the cleavage locus showed that both basic residues are critically
important, whereas Glu12 is not. It is proposed that S-28 processing
involves a divalent cation-sensitive endoprotease that is sensitive to
thiol reagents, which cleaves before the Arg-Lys doublet, which is not
trypsin-like, and whose action is coupled to an aminopeptidase B-like
enzyme.

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Copyright © 1987 by the American Society for Biochemistry and Molecular Biology.
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