Department of Molecular Biology, University of Wyoming, 1000 E. University Ave., Laramie, WY 82072, USA.
Amino Acids. 2013 Aug;45(2):359-67. doi: 10.1007/s00726-013-1509-x. Epub 2013 May 21.
Tyrosine depletion in metazoan proteins was recently explained to be due to the appearance of tyrosine kinases in Metazoa. Here, we present a complementary explanation for the depletion of tyrosine, stating the importance of tyrosine in signaling not only as a phosphorylation target but also as a precursor for catecholamines and hormones. Molecules (dopamine, norepinephrine, and epinephrine, and to a lesser extent serotonin and melatonin) critical to metazoan multicellular signaling are also greatly dependent on a supply of tyrosine. These signaling molecules are synthesized in two highly linked pathways specific to metazoans. In addition, the shikimate pathway that non-metazoans use to synthesize the aromatic amino acids is not present in metazoans. These important pathway changes have occurred between Metazoa and other eukaryotes, causing significant changes to tyrosine metabolism and rendering tyrosine crucial for extracellular signaling. In addition, the evolutionary and functional linkage between these two pathways and the resulting implications for neuropathology are discussed.
最近有研究表明，后生动物蛋白中的酪氨酸缺失是由于后生动物中酪氨酸激酶的出现。在这里，我们提出了一种酪氨酸缺失的补充解释，指出酪氨酸在信号传递中的重要性不仅体现在作为磷酸化靶标，还体现在作为儿茶酚胺和激素的前体。对于后生动物多细胞信号传递至关重要的分子（多巴胺、去甲肾上腺素和肾上腺素，在较小程度上还有血清素和褪黑素）也极大地依赖于酪氨酸的供应。这些信号分子是在两条高度连锁的特定于后生动物的途径中合成的。此外，非后生动物用于合成芳香族氨基酸的莽草酸途径在后生动物中不存在。这些重要的途径变化发生在后生动物和其他真核生物之间，导致酪氨酸代谢发生重大变化，使酪氨酸对细胞外信号传递至关重要。此外，还讨论了这两条途径之间的进化和功能联系，以及它们对神经病理学的影响。
