A new type of the human TSA homologous gene was cloned from a HeLa cell cDNA and characterized. The gene product consists of 161 amino acids with a molecular mass of 16,900. The TSA homologous protein, as a new 6th member of the human TSA (hTSA VI), exerted a thiol-dependent peroxidase activity with the use of thioredoxin system as a physiological electron donor. The values of Vmax/ Km of hTSA VI for H2O2 and t-butyl hydroperoxide (t-BOOH) were calculated as 5.53×10-2 and 3.70×10-2, respectively. This implies that hTSA VI is a peroxidase, which reduces H2O2 and t-BOOH. The mutation of Cys47 to serine resulted in a complete loss of the peroxidase activity. This suggests that Cys47 acts as a primary site of catalysis. The analysis of the tryptic digest derived from hTSA VI revealed that the Cys47 exists as a free thiol form. Taken together, these results suggest that the TSA homologous protein is a new type of the human family, which exerts thioredoxin-linked peroxidase activity toward H2O2 and alkyl hydroperoxide.
|Number of pages||8|
|Journal||Journal of Biochemistry and Molecular Biology|
|State||Published - 31 May 2000|
- Functional cysteine
- New human thiol peroxidase
- Reactive oxygen species