PMID: 2104844Jan 25, 1990Paper

Enzymic properties of thermopsin.

The Journal of Biological Chemistry
M FusekJ Tang

Abstract

The specificity of thermopsin, a thermostable acid protease from Sulfolobus acidocaldarius, was studied using oxidized insulin B chain as substrate followed by peptide isolation and identification. The following bonds were hydrolyzed: Leu-Val, Leu-Tyr, Phe-Phe, Phe-Tyr, and Tyr-Thr. Thus, the specificity of thermopsin is similar to that of pepsin, that is, it prefers large hydrophobic residues at both sides of the scissile bond. We confirmed this by the use of a synthetic substrate, Lys-Pro-Ala-Glu-Phe-p-nitro-phenylalanyl-Ala-Leu, which was cleaved by thermopsin between Phe and p-nitro-phenylalanyl. Using this substrate, enzyme inhibition and kinetic properties of thermopsin have been studied. Thermopsin optimally hydrolyzes this substrate at 75 degrees C and pH 2 with Km and kcat values under these conditions of 5.3 x 10(-5) M and 14.3 s-1, respectively. Pepstatin competitively inhibits thermopsin with a Ki of 2 x 10(-7) M. Other known aspartic protease inhibitors, diazoacetylnorleucine ethyl ester and 1,2-epoxy-3-(p-nitrophenoxy)propane inhibited thermopsin only slowly and with nonspecific reactions. Although thermopsin contains a single cysteine, iodoacetic acid and p-chloromercuric benzoate had no effect on activity. Mercu...Continue Reading

Related Concepts

Related Feeds

ASBMB Publications

The American Society for Biochemistry and Molecular Biology (ASBMB) includes the Journal of Biological Chemistry, Molecular & Cellular Proteomics, and the Journal of Lipid Research. Discover the latest research from ASBMB here.