MIP and cataract: Two CaM molecules bind to the AQP0 tetramer in the presence of calcium14 and the binding of CaM to the C‐terminus of AQP0 can be regulated by phosphorylation, whereby phosphorylation decreases the affinity of AQP0 for CaM 20‐ to 50‐fold.16 The inhibition of water flow upon CaM binding is suggested to work by cooperativity between adjacent subunits in an allosteric fashion17 and a point mutation which causes polymorphic congenital cataract (R233K) gives rise to a weaker interaction with CaM.18