And that's why we call it an integral protein. So if we basically change our PH or add a salt solution this will not dissociate because a good portion of it actually is permanently bound to that cell membrane. Now, where do we find these molecules? Well, typically, we find them in the membrane of the endoplasmic reticulum, and this portion basically points into the aqueous environment of the lumen of the endoplasm reticulum. So this is a cytoplasm and this is the endoplasm reticulum. Now, what's the function of this protein?