Tarantula hemocyanin shows phenoloxidase activity

被引:188
作者
Decker, H [1 ]
Rimke, T [1 ]
机构
[1] Univ Mainz, Inst Mol Biophys, D-55128 Mainz, Germany
关键词
D O I
10.1074/jbc.273.40.25889
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
An enzyme generally catalyzes one well defined reaction with high specificity and efficiency. We report here in contrast that the copper protein hemocyanin of the tarantula Eurypelma californicum exhibits two different functions. These occur at the same active site. While hemocyanin usually is an oxygen carrier, its function can be transformed totally to monophenoloxidase and o-diphenoloxidase activity after limited proteolysis with trypsin or chymotrypsin, N-acetyldopamine (NADA) is more effectively oxidized than L-dopa or dopamine. This irreversible functional switch of tarantula hemocyanin function is limited to the two subunits b and c of its seven subunit types. A conserved phenylalanine in the hemocyanin molecule acts as a placeholder for other substrates that are phenylalanine derivatives. The proteolytic cleavage removes an N-terminal fragment, including the critical phenylalanine residue, which opens an entrance for substrates. Therefore no new arrangement of the active site, with its two copper atoms and the mu - eta(2):eta(2) bound O-2 molecule, is necessary to develop the catalytic function.
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页码:25889 / 25892
页数:4
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