cctα is an amphitropic enzyme, meaning that it exists as either an inactive soluble form, or an active, membrane bound form. whether or not cctα is membrane bound is largely dictated by the relative composition of membranes. if membranes are low in pc, and relatively enriched in anionic lipids, diacylglycerol, or phosphatidylethanolamine, cct inserts into the membrane bilayer via its membrane binding domain. this binding event relieves an autoinhibitory constraint on the catalytic domain, resulting in a decrease in the km for phosphocholine.