pt ides ▁that ▁are ▁derived ▁from ▁the ▁ven om ▁of ▁pre dat ory ▁marine ▁sn ails ▁of ▁the ▁genus ▁Con us . ▁Con ant ok ins ▁act ▁as ▁pot ent ▁and ▁specific ▁ant agon ists ▁of ▁the ▁N - m eth yl - D - as part ate ▁re ceptor ▁( N MD AR ). ▁They ▁are ▁the ▁only ▁naturally - der ived ▁pe pt ides ▁to ▁do ▁so . ▁The ▁sub types ▁of ▁con ant ok ins ▁exhib it ▁a ▁surprising ▁vari ability ▁of ▁select ivity ▁across ▁the ▁N MD AR ▁sub un its , ▁and ▁are ▁therefore ▁uniqu ely ▁useful ▁in ▁developing ▁sub unit - specific ▁ph arm ac ological ▁prob es . ▁ ▁Chem ically , ▁con ant ok ins ▁are ▁unique ▁in ▁that ▁they ▁possess ▁a ▁number ▁( gener ally ▁ 4 ▁or ▁ 5 ) ▁of ▁g amma - car box y gl ut am yl ▁( G la ) ▁resid ues , ▁generated ▁by ▁the ▁post - trans l ational ▁modification ▁of ▁gl ut am yl ▁( G lu ) ▁resid ues . ▁These ▁Gla ▁resid ues ▁indu ce ▁a ▁conform ational ▁change ▁from ▁a ▁ 3 ▁ 1 0 ▁hel ix ▁to ▁an ▁alpha ▁hel ix ▁on ▁binding ▁to ▁Cal ci um . ▁In ▁the ▁bro ader ▁scheme ▁of ▁gen etic ▁con ot ox in ▁classification , ▁Con an ot ok ins ▁are ▁also ▁known ▁as ▁" Con ot ox in ▁Super family ▁B ." ▁ ▁The ▁word ▁" con ant ok in " ▁is ▁derived