ney , ▁the ▁jej unal ▁br ush ▁border ▁of ▁the ▁small ▁int est ine ▁and ▁gang lia ▁of ▁the ▁nerv ous ▁system . ▁ ▁Indeed , ▁the ▁initial ▁cl oning ▁of ▁the ▁c D NA ▁encoding ▁the ▁gene ▁express ing ▁PS MA ▁was ▁accomplished ▁with ▁R NA ▁from ▁a ▁pro state ▁tum or ▁cell ▁line , ▁L NC a P . ▁PS MA ▁shares ▁hom ology ▁with ▁the ▁transfer rin ▁re ceptor ▁and ▁under go es ▁end oc yt osis ▁but ▁the ▁lig and ▁for ▁indu cing ▁internal ization ▁has ▁not ▁been ▁identified . ▁It ▁was ▁found ▁that ▁PS MA ▁was ▁the ▁same ▁as ▁the ▁memb rane ▁protein ▁in ▁the ▁small ▁int est ine ▁responsible ▁for ▁removal ▁of ▁g amma - link ed ▁gl ut am ates ▁from ▁pol yg amm ag l ut am ate ▁fol ate . ▁ ▁This ▁enables ▁the ▁free ing ▁of ▁fol ic ▁acid , ▁which ▁then ▁can ▁be ▁transport ed ▁into ▁the ▁body ▁for ▁use ▁as ▁a ▁vit amin . ▁This ▁resulted ▁in ▁the ▁cl oned ▁genom ic ▁design ation ▁of ▁PS MA ▁as ▁F OL H 1 ▁for ▁fol ate ▁hyd rol ase . ▁ ▁PS MA ( F OL H 1 )+ ▁fol ate ▁pol yg amm ag l ut am ate ( n ▁ 1 - 7 )-- -> ▁PS MA ▁( F OL H 1 ) ▁+ ▁fol ate ( poly ) g amm ag l ut am ate ( n - 1 ) ▁+ ▁gl ut am ate ▁continu ing ▁until ▁re