Yokota E, Riggs A F
J Biol Chem. 1984 Apr 25;259(8):4739-49.
The amino acid sequence of the largest CNBr fragment, CNBrIa, from hemocyanin II of Limulus polyphemus has been determined. This fragment contains 203 residues, has Mr = 23,600, and is the NH2-terminal segment of the molecule. Comparison of this sequence with the first 87 residues of the NH2-terminal sequence of the alpha chain of hemocyanin from the Japanese horseshoe crab, Tachypleus tridentatus, of the Western Pacific (Nemoto, T., and Takagi, T. (1981) Biochim. Biophys. Acta 670, 79-83) shows that 46% of the residues are identical. Residues 172-177, -His-His-Trp-His-Trp-His-, appear to constitute at least part of the copper-binding site. This conclusion is supported by our finding that 40% of the residues in the sequence 172-186 are identical to residues 188-202 in tyrosinase from Neurospora; residues 188 and 193 in tyrosinase are known to be copper-binding histidines (Pfiffner, E., and Lerch, K. (1981) Biochemistry 20, 6029-6035). Model building suggests that histidines 172 and 175 might bind one copper atom and histidines 173 and 177 might bind the second copper. These observations suggest that tyrosinase and hemocyanin may have a common evolutionary origin, but we have not so far seen other correspondences.
已确定来自美洲鲎血蓝蛋白II的最大溴化氰片段CNBrIa的氨基酸序列。该片段包含203个残基，Mr = 23,600，是该分子的NH2末端片段。将此序列与西太平洋日本鲎（Tachypleus tridentatus）血蓝蛋白α链NH2末端序列的前87个残基进行比较（Nemoto, T., and Takagi, T. (1981) Biochim. Biophys. Acta 670, 79 - 83），结果显示46%的残基相同。残基172 - 177，-His-His-Trp-His-Trp-His-，似乎构成了至少部分铜结合位点。我们发现序列172 - 186中的40%残基与链孢霉酪氨酸酶中188 - 202位残基相同，这一发现支持了该结论；已知酪氨酸酶中的残基188和193是结合铜的组氨酸（Pfiffner, E., and Lerch, K. (1981) Biochemistry 20, 6029 - 6035）。模型构建表明，组氨酸172和175可能结合一个铜原子，组氨酸173和177可能结合第二个铜原子。这些观察结果表明酪氨酸酶和血蓝蛋白可能有共同的进化起源，但到目前为止我们尚未发现其他对应关系。
