ase ▁is ▁a ▁my elin - associ ated ▁en zym e ▁that ▁makes ▁up ▁ 4 % ▁of ▁total ▁C NS ▁my elin ▁protein , ▁and ▁is ▁thought ▁to ▁under go ▁significant ▁age - associ ated ▁changes . ▁It ▁is ▁named ▁for ▁its ▁ability ▁to ▁catal y ze ▁the ▁ph osph odi ester ▁hydro ly s is ▁of ▁ 2 ', 3 '- cyc lic ▁nucle ot ides ▁to ▁ 2 '- n uc le ot ides , ▁though ▁a ▁coh es ive ▁understanding ▁of ▁its ▁specific ▁phys i olog ic ▁functions ▁are ▁still ▁ambigu ous . ▁ ▁Struct ural ▁studies ▁have ▁revealed ▁that ▁four ▁classes ▁of ▁C NP ases ▁belong ▁to ▁one ▁protein ▁super family . ▁C NP ase ' s ▁catal yt ic ▁core ▁consists ▁of ▁three ▁alpha - hel ices ▁and ▁nine ▁beta - str ands . ▁The ▁proposed ▁mechanism ▁of ▁C NP ases ▁ph osph odi ester ase ▁catal yt ic ▁activity ▁is ▁similar ▁to ▁the ▁second ▁step ▁of ▁the ▁reaction ▁mechanism ▁for ▁R N ase ▁A . ▁ ▁C NP ase ▁is ▁expressed ▁exclus ively ▁by ▁o lig od end ro cy tes ▁in ▁the ▁C NS , ▁and ▁the ▁appearance ▁of ▁C NP ase ▁seems ▁to ▁be ▁one ▁of ▁the ▁earliest ▁events ▁of ▁o lig od end ro cy te ▁different iation . ▁C NP ase ▁is ▁thought ▁to ▁play ▁a ▁critical ▁role ▁in ▁the ▁events ▁leading ▁up ▁to ▁my el ination . ▁ ▁C NP ase ▁also ▁associ ates ▁with ▁micro t ub ules ▁in ▁brain