ains ▁of ▁other ▁polar ▁am ino ▁ac ids . ▁However , ▁the ▁c yst e ine ▁side ▁chain ▁has ▁been ▁shown ▁to ▁stabil ize ▁hydro ph ob ic ▁interactions ▁in ▁mic elles ▁to ▁a ▁greater ▁degree ▁than ▁the ▁side ▁chain ▁in ▁the ▁non pol ar ▁am ino ▁acid ▁g ly c ine ▁and ▁the ▁polar ▁am ino ▁acid ▁ser ine . ▁In ▁a ▁statistical ▁analysis ▁of ▁the ▁frequency ▁with ▁which ▁am ino ▁ac ids ▁appear ▁in ▁different ▁chemical ▁environments ▁in ▁the ▁structures ▁of ▁prote ins , ▁free ▁c yst e ine ▁resid ues ▁were ▁found ▁to ▁associate ▁with ▁hydro ph ob ic ▁regions ▁of ▁prote ins . ▁Their ▁hydro ph ob ic ▁t endency ▁was ▁equivalent ▁to ▁that ▁of ▁known ▁non pol ar ▁am ino ▁ac ids ▁such ▁as ▁m eth ion ine ▁and ▁ty ros ine ▁( ty ros ine ▁is ▁polar ▁a rom atic ▁but ▁also ▁hydro ph ob ic ), ▁those ▁of ▁which ▁were ▁much ▁greater ▁than ▁that ▁of ▁known ▁polar ▁am ino ▁ac ids ▁such ▁as ▁ser ine ▁and ▁thre on ine . ▁H ydro ph ob icity ▁scales , ▁which ▁rank ▁am ino ▁ac ids ▁from ▁most ▁hydro ph ob ic ▁to ▁most ▁hydro ph il ic , ▁consist ently ▁place ▁c yst e ine ▁towards ▁the ▁hydro ph ob ic ▁end ▁of ▁the ▁spectrum , ▁even ▁when ▁they ▁are ▁based ▁on ▁methods ▁that ▁are ▁not ▁influenced ▁by ▁the ▁t endency ▁of ▁c yst e ines ▁to ▁form ▁dis ulf ide ▁b onds ▁in ▁prote ins . ▁Therefore