▁in ▁turn , ▁could ▁represent ▁the ▁varying ▁degrees ▁of ▁flex ib ilities ▁allowed ▁by ▁these ▁kin ases ' ▁catal yt ic ▁ATP - binding ▁sites . ▁ ▁Bi ological ▁activities ▁ ▁Bal an ol ▁is ▁one ▁of ▁the ▁most ▁pot ent , ▁naturally ▁occurr ing ▁in hib itors ▁of ▁protein ▁kin ases ▁PK C ▁and ▁PK A . ▁Bal an ol ▁was ▁originally ▁discovered ▁to ▁in hib it ▁PK C ▁and ▁many ▁of ▁its ▁is o forms ▁in ▁humans ▁( α , ▁ β - Ι , ▁ β - Ι Ι , ▁ γ , ▁ δ , ▁ ε , ▁ η ), ▁with ▁an ▁in hib ition ▁profile ▁similar ▁to ▁that ▁of ▁st au ro sp or ine . ▁▁▁ <0x09> ▁Bal an ol ▁prevents ▁function ing ▁by ▁binding ▁compet it ively ▁to ▁the ▁catal yt ic ▁domain ▁of ▁PK C ▁and ▁PK A ▁with ▁an ▁aff inity ▁( K i ▁ ≥ ▁ 4 n M ) ▁three ▁orders ▁of ▁magnitude ▁greater ▁than ▁for ▁ATP . ▁Without ▁ATP ▁bound , ▁these ▁kin ases ▁are ▁unable ▁to ▁catal y ze ▁the ▁transfer ▁of ▁the ▁ γ - ph osph ate ▁from ▁ATP ▁to ▁the ▁kin ase ' s ▁target ▁substr ate , ▁and ▁thus ▁function ▁is ▁h inder ed . ▁ ▁Binding ▁B ound ▁bal an ol ▁extends ▁ 1 7 . 2 ▁Å ▁from ▁the ▁hydro x yl ▁o xygen ▁atom ▁of ▁its ▁ 4 - h ydro xy ben z am ide ▁to ▁the ▁most ▁dist al ▁car