Lehman H K, Murgiuc C M, Hildebrand J G
Department of Biological Sciences, Hamilton College, Clinton, NY 13323, USA.
Insect Biochem Mol Biol. 2000 May;30(5):377-86. doi: 10.1016/s0965-1748(00)00011-4.
Octopamine (OA) is present in insect nervous tissue, but little is known about its biosynthesis. In the CNS of Manduca sexta, OA levels increase markedly during postembryonic adult development. To study this increase, we developed an assay for tyramine-beta-hydroxylase, the putatively rate-limiting enzyme for OA biosynthesis. Tyramine-beta-hydroxylase activity in extracts of M. sexta CNS tissue: (1) was time- and protein-dependent, and with protein concentrations up to 2 microg/microl, was linear for 20 min; (2) had a pH optimum of 7.0 for conversion of tyramine to OA; (3) required ascorbate, copper, and catalase; and (4) had an apparent K(M, tyramine) of 0.22+/-0.04 mM. These characteristics resemble those of the mammalian enzyme dopamine-beta-hydroxylase, suggesting that these two enzymes are functionally related. During adult development, tyramine-beta-hydroxylase activity increased 11-fold in the brain and 9-fold in the abdominal ganglia, paralleling increases in OA levels in those CNS structures during metamorphosis. The apparent kinetic constants of tyramine-beta-hydroxylase suggested that the amount of this enzyme present in the tissues increases. The increase in OA levels during adult development thus appears to be due to an increase in the level of enzyme available for OA synthesis and may reflect an increase in the number of octopaminergic neurons.
章鱼胺（OA）存在于昆虫神经组织中，但其生物合成过程却鲜为人知。在烟草天蛾的中枢神经系统（CNS）中，章鱼胺水平在胚胎后成虫发育过程中显著增加。为了研究这种增加，我们开发了一种用于测定酪胺-β-羟化酶的方法，该酶被认为是章鱼胺生物合成的限速酶。烟草天蛾中枢神经系统组织提取物中的酪胺-β-羟化酶活性：（1）具有时间和蛋白质依赖性，在蛋白质浓度高达2微克/微升时，20分钟内呈线性；（2）将酪胺转化为章鱼胺的最适pH值为7.0；（3）需要抗坏血酸、铜和过氧化氢酶；（4）酪胺的表观米氏常数（K(M, tyramine)）为0.22±0.04毫摩尔。这些特性与哺乳动物的多巴胺-β-羟化酶相似，表明这两种酶在功能上相关。在成虫发育过程中，酪胺-β-羟化酶活性在脑中增加了11倍，在腹神经节中增加了9倍，与变态过程中这些中枢神经系统结构中章鱼胺水平的增加平行。酪胺-β-羟化酶的表观动力学常数表明，组织中该酶的含量增加。因此，成虫发育过程中章鱼胺水平的增加似乎是由于可用于章鱼胺合成的酶水平增加，这可能反映了章鱼胺能神经元数量的增加。
