Olianas Alessandra, Sanjust Enrico, Pellegrini Mariagiuseppina, Rescigno Antonio
Department of Sciences Applied to Biosystems, University of Cagliari, Cittadella Universitaria, 09042, Monserrato (CA), Italy.
J Comp Physiol B. 2005 Aug;175(6):405-11. doi: 10.1007/s00360-005-0002-6. Epub 2005 Jul 12.
The respiratory protein hemocyanin is present in molluscans and in some species of arthropods, and its dioxygen binding site strongly resembles that of the monophenol-hydroxylating and catechol-quinonising enzyme tyrosinase. Moreover, some hemocyanins show a certain extent of tyrosinase activity, so a common ancestry between the two proteins has been suggested. However, in the case purified hemocyanin of Scyllarides latus any attempts to evoke tyrosinase activity failed. A distinct tyrosinase has been purified to homogeneity from the hemolymph, and kinetically characterised. The purified tyrosinase showed both monophenolase and diphenolase enzyme activity and therefore it could be well defined as a true tyrosinase. This finding suggests that in the case of the studied crustacean the evolutionary functional divergence between dioxygen transport and oxidation of phenolics has already reached its completeness.
呼吸蛋白血蓝蛋白存在于软体动物和某些节肢动物物种中，其双氧结合位点与单酚羟化和儿茶酚醌化酶酪氨酸酶的双氧结合位点极为相似。此外，一些血蓝蛋白表现出一定程度的酪氨酸酶活性，因此有人提出这两种蛋白质有共同的祖先。然而，就纯化的宽甲藻虾血蓝蛋白而言，任何激发酪氨酸酶活性的尝试均告失败。一种独特的酪氨酸酶已从血淋巴中纯化至同质，并进行了动力学表征。纯化的酪氨酸酶同时表现出单酚酶和双酚酶活性，因此可以明确地定义为一种真正的酪氨酸酶。这一发现表明，在所研究的甲壳类动物中，双氧运输和酚类氧化之间的进化功能差异已经达到了完全程度。
