Hi me again,
Anything it doesn't like and the stupid thing will precipitate. Anything away from the pI [1] (isoelectric point) will do the trick- which seems to be what you are after. In fact it can be pretty hard to keep a protein IN solution

(sorry sore point). Just alter the pH of the solution your protein is dissolved in with something like NaOH, or HCl - or in fact anything that is a acid or a base should do it.
What is this for? What level are you studing at/what course? Just seems like a pretty random question, I'm not sure you are understanding your course very well. Perhaps you should speak to an advisor/teacher/lecturer to see where you can get some help.
I can try to help on here but nothing beats face to face tuition. Whatever you do don't leave things until right before the exams or it'll be a nightmare.
Good luck- hope you are getting on alright with your glucose curve question.
1)
Isoelectric point - Wikipedia, the free encyclopedia Protein Precipitation