The present invention relates to a method or process for controlling, inhibiting or reducing protein fucosylation in a eukaryote and/or a eukaryotic protein expression system. Said method comprises carrying out the protein expression and/or post-translational modification in the presence of an elevated total concentration of manganese or manganese ions.本發明與一種用於控制、抑制或減少真核動物及/或真核動物的蛋白質表現系統中蛋白質岩藻糖基化的方法或過程有關。該方法包括在一提高的總錳或錳離子濃度存在下進行蛋白質表現及/或轉譯後修飾。