请问 by which 定语从句,by 是在从句什么位置提前了?

问题描述:

请问 by which 定语从句,by 是在从句什么位置提前了?
Nicklin et al.describe a mechanism by which glutamine facilitates the uptake of leucine,leading to receptor activation

虽然看不懂很多单词是什么意思 但按照句子结构应该是 the glutamine facilitates the uptake of leucine by mechanism