▁the ▁ 2 1 st ▁am ino ▁acid ▁s elen oc yst e ine ▁is ▁inserted ▁in ▁the ▁nas cent ▁pol ype pt ide ▁chain ▁during ▁the ▁process ▁of ▁transl ational ▁rec oding ▁of ▁the ▁U GA ▁stop ▁cod on . ▁In ▁addition ▁to ▁the ▁U GA - cod on , ▁a ▁c is - act ing ▁element ▁in ▁the ▁m R NA , ▁called ▁SE C IS , ▁bind s ▁S B P 2 ▁to ▁rec ruit ▁other ▁prote ins , ▁such ▁as ▁e uk ary otic ▁el ong ation ▁factor ▁s elen oc yst e ine - t R NA ▁specific , ▁to ▁form ▁the ▁complex ▁responsible ▁for ▁the ▁rec oding ▁process . ▁ ▁The ▁protein ▁encoded ▁by ▁this ▁gene ▁forms ▁a ▁hom ot et ram er ▁structure . ▁As ▁with ▁other ▁gl ut ath ione ▁per ox id ases , ▁GP x 1 ▁has ▁a ▁conser ved ▁catal yt ic ▁t et rad ▁composed ▁of ▁Sec ▁or ▁C ys , ▁G ln , ▁Tr p , ▁and ▁As n , ▁where ▁the ▁Sec ▁is ▁surrounded ▁by ▁four ▁arg in ines ▁( R ▁ 5 7 , ▁ 1 0 3 , ▁ 1 8 4 , ▁ 1 8 5 ; ▁b ov ine ▁number ing ) ▁and ▁a ▁l ys ine ▁of ▁an ▁adjacent ▁sub unit ▁( K ▁ 9 1 '). ▁These ▁ 5 ▁resid ues ▁bind ▁gl ut ath ione ▁( G SH ) ▁and ▁are ▁only ▁present ▁in ▁GP x 1 . ▁ ▁Two ▁altern atively