期刊
CHEMBIOCHEM
卷 13, 期 2, 页码 193-201出版社
WILEY-BLACKWELL
DOI: 10.1002/cbic.201100609
关键词
copper; dioxygen activation; enzyme function; hemocyanin; proenzymes; tyrosinases
资金
- MEXT, Japan [20350082, 20038784]
- Mitsubishi Foundation
- Nagase Science and Technology Foundation
- Shorai Foundation for Science and Technology
- Grants-in-Aid for Scientific Research [20350082, 21750181] Funding Source: KAKEN
The pro form of melB tyrosinase from the melB gene of Aspergillus oryzae was over-produced from E. coli and formed a homodimer that exhibited the spectral features of met-tyrosinase. In the presence of NH2OH (reductant), the proenzyme bound dioxygen to give a stable (mu-eta(2):eta(2)-peroxo)dicopper(II) species (oxy form), thus indicating that the pro form tyrosinase can function as an oxygen carrier or storage protein like hemocyanin. The pro form tyrosinase itself showed no catalytic activity toward external substrates, but proteolytic digestion with trypsin activated it to induce tyrosinase activity. Mass spectroscopy analyses, mutagenesis experiments, and colorimetry assays have demonstrated that the tryptic digestion induced cleavage of the C-terminal domain (Glu458-Ala616), although the dimeric structure of the enzyme was retained. The structural changes induced by proteolytic digestion might open the entrance to the enzyme active site for substrate incorporation.
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