Yokoyama Chiaki, Takei Mami, Kouzuma Yoshiaki, Nagata Shinji, Suzuki Yoshihito
Department of Food and Life Sciences, Ibaraki University, 3-21-1 Chuo, Ami-machi, Inashiki, Ibaraki 300-0393, Japan.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-city, Chiba 277-8567, Japan.
J Insect Physiol. 2017 Aug;101:91-96. doi: 10.1016/j.jinsphys.2017.07.006. Epub 2017 Jul 18.
In the course of our study of the biosynthetic pathway of auxin, a class of phytohormones, in insects, we proposed the biosynthetic pathway tryptophan (Trp)→indole-3-acetaldoxime (IAOx)→indole-3-acetadehyde (IAAld)→indole-3-acetic acid (IAA). In this study, we identified two branches in the metabolic pathways in the silkworm, possibly affecting the efficiency of IAA production: Trp→indole-3-pyruvic acid→indole-3-lactic acid and IAAld→indole-3-ethanol. We also determined the apparent conversion activities (2.05×10UmL for Trp→IAA, 1.30×10UmL for IAOx→IAA, and 3.91×10UmL for IAAld→IAA), which explain why IAOx and IAAld are barely detectable as either endogenous compounds or metabolites of their precursors. The failure to detect IAAld, even in the presence of an inhibitor of the conversion IAAld→IAA, is explained by a switch in the conversion from IAAld→IAA to IAAld→IEtOH.
在我们对昆虫中一类植物激素生长素的生物合成途径的研究过程中，我们提出了生物合成途径：色氨酸（Trp）→吲哚 - 3 - 乙醛肟（IAOx）→吲哚 - 3 - 乙醛（IAAld）→吲哚 - 3 - 乙酸（IAA）。在本研究中，我们在蚕的代谢途径中鉴定出两个分支，可能会影响IAA的产生效率：Trp→吲哚 - 3 - 丙酮酸→吲哚 - 3 - 乳酸和IAAld→吲哚 - 3 - 乙醇。我们还测定了表观转化活性（Trp→IAA为2.05×10U/mL，IAOx→IAA为1.30×10U/mL，IAAld→IAA为3.91×10U/mL），这解释了为什么IAOx和IAAld作为内源性化合物或其前体的代谢产物几乎检测不到。即使存在IAAld→IAA转化的抑制剂时也未能检测到IAAld，这是由于转化从IAAld→IAA切换到了IAAld→IEtOH所致。
