Enzymes Have properties shared by all catalysts Enhance the rates of both forward and reverse reactions so equilibrium is achieved more rapidly Position of equilibrium is unchanged Reduce activation energy Not permanently altered during the reaction Can act over and over again = catalytically Have unique properties Exhibit extreme substrate (reactant) specificity Exhibit reaction specificity, no side reactions Can couple reactions Can be regulated

Michaelis-Menten Plot V max [S] v o = K m + [S]

Enzyme Regulation See both positive and negative regulation Small molecules interact with enzyme Can bind to E to affect binding of S to form ES Can bind to ES to affect conversion of S to P

Reversible Inhibition Competitive inhibition I competes with S for binding to E

Competitive Inhibition

Benzamidine competes with arginine for binding to trypsin

Statins are competitive inhibitors of cholesterol synthesis

Competitive Inhibition

Reversible Inhibition Competitive inhibition I competes with S for binding to E V max unaffected, but K m increases

Reversible Inhibition Competitive inhibition I competes with S for binding to E V max unaffected, but K m increases Uncompetitive inhibition I binds to ES and blocks formation of P

Uncompetitive Inhibition

Reversible Inhibition Competitive inhibition I competes with S for binding to E V max unaffected, but K m increases Uncompetitive inhibition I binds to ES and blocks formation of P Both V max and K m decrease proportionally

Reversible Inhibition Competitive inhibition I competes with S for binding to E V max unaffected, but K m increases Uncompetitive inhibition I binds to ES and blocks formation of P Both V max and K m decrease proportionally Noncompetitive inhibition I can bind to either E or ES

Noncompetitive Inhibition

Reversible Inhibition Competitive inhibition I competes with S for binding to E V max unaffected, but K m increases Uncompetitive inhibition I binds to ES and blocks formation of P Both V max and K m decrease proportionally Noncompetitive inhibition I can bind to either E or ES V max reduced, K m unaffected