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The Journal of Biochemistry
Year: 2010  |  Volume: 147  |  Issue: 4  |  Page No.: 485 - 492

The optimal activity of a pseudozymogen form of recombinant matriptase under the mildly acidic pH and low ionic strength conditions

K Inouye, M Yasumoto, S Tsuzuki, S Mochida and T. Fushiki    

Abstract:

Matriptase is a transmembrane serine protease that is strongly expressed in epithelial cells. The single-chain zymogen of matriptase is considered to have inherent activity, leading to its own activation (i.e. conversion to the disulphide-linked-two-chain form by cleavage after Thr–Lys–Gln–Ala–Arg614). Also, there is growing evidence that the activation of zymogen occurs at the cell surface and in relation to the acidification and lowering of ionic strength within cell-surface microenvironments. The present study aimed to provide evidence for the involvement of zymogen activity in its activation in physiologically relevant cellular contexts. For this purpose, the activity of a pseudozymogen form of recombinant matriptase (HL-matriptase zymogen) was examined using acetyl-l-Lys–l-Thr–l-Lys–l-Gln–l-Leu–l-Arg–4-methyl-coumaryl-7-amide as a substrate. HL-matriptase zymogen exhibited optimal activity toward the substrate pH ~6.0. The substrate hydrolysis at the pH value was hardly detected when NaCl was present at a concentration of 145 mM. In a buffer of pH 6.0 containing 5 mM NaCl, the activity of HL-matriptase zymogen was only ~30-times lower than that of the respective two-chain form. These findings suggest that the in vivo activation of matriptase zymogen occurs via a mechanism involving the zymogen activity.

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