Dear colleagues, i hope every one doing well. i am trying to remove the 10x his tag , as i tried to crystallize with the tag but i didn^t obtain crystals unless some salt crystals , very small crystals and some precipitant. i want to use factor 10a protease but i didn^t tried it before. this is the first time for using it. i have factor 10a protease from Qiagen 400 unit . i have read the protocol but i still need some suggestion and experience as you know it is expensive. also i have another question , how many protein digested by one unit ? i know it depend but roughly how much? i really appreciate your support. best regards Amr