In some cells they're recycled, that is the cell is able to take up the neurotransmitter after it's released and restore it, but most often there are enzyme systems inside the pre-synaptic membrane where those neurotransmitters are synthesized.

在一些细胞中神经递质可以循环利用,这些细胞可以吸收,已经释放出的神经递质并重新储存起来,但更常见的是突触前膜中含有酶系统,在此合成神经递质

耶鲁公开课 - 生物医学工程探索课程节选

The first three letters of E. Coli are Eco, so Eco.

大肠杆菌的前三个字母是Eco,也就是酶名字中的Eco

耶鲁公开课 - 生物医学工程探索课程节选