Well, cysteine is that amino acid that can participate in forming disulfide bridges. And not only that, it has a PK of 8.3. And what that means is, if we're at 8.3, if our PH is at zero point, 350 percent will exist in this form, and the remaining will exist in this negatively charged form. So if we're in a very basic solution, let's say a solution with a PH of ten, all of our cysteine molecules will predominate, will exist in this ion form, and this will be able to form ionic bonds with positively charged species. Now, lying, tyrosine and arginine have a very basic PKA value. It's above ten.