ase , ▁a ▁transm emb rane ▁ant ip orter . ▁ ▁The ▁exact ▁mechanism ▁used ▁by ▁sul f otr ans fer ases ▁is ▁still ▁being ▁el uc id ated , ▁but ▁studies ▁have ▁indicated ▁that ▁sul f otr ans fer ases ▁use ▁an ▁in - line ▁sul fony l - trans fer ▁mechanism ▁that ▁is ▁analog ous ▁to ▁the ▁ph osph ory l ▁transfer ▁mechanism ▁used ▁by ▁many ▁kin ases , ▁which ▁is ▁logical ▁given ▁the ▁great ▁level ▁of ▁struct ural ▁and ▁functional ▁similar ities ▁between ▁kin ases ▁and ▁sul f otr ans fer ases ▁( Fig ure ▁ 2 ). ▁In ▁car bo h yd rate ▁sul f otr ans fer ases ▁a ▁conser ved ▁l ys ine ▁has ▁been ▁identified ▁in ▁the ▁active ▁P AP S ▁binding ▁site , ▁which ▁is ▁analog ous ▁to ▁a ▁conser ved ▁l ys ine ▁in ▁the ▁active ▁ATP ▁binding ▁site ▁of ▁kin ases . ▁Prote in ▁sequence ▁alignment ▁studies ▁indicate ▁that ▁this ▁l ys ine ▁is ▁conser ved ▁in ▁c yt os ol ic ▁sul f otr ans fer ases ▁as ▁well . ▁ ▁In ▁addition ▁to ▁the ▁conser ved ▁l ys ine , ▁sul f otr ans fer ases ▁have ▁a ▁highly ▁conser ved ▁hist id ine ▁in ▁the ▁active ▁site . ▁Based ▁on ▁the ▁conservation ▁of ▁these ▁resid ues , ▁theoretical ▁models , ▁and ▁experimental ▁measurements ▁a ▁theoretical ▁transition ▁state ▁for ▁catal yz ed ▁sul f ation ▁has ▁been ▁proposed ▁( Fig ure ▁ 3 ). ▁ ▁Bi ological ▁function ▁Car bo h