Basics of Biochemistry Enzyme Inhibition Ashish Kr Dwivedi, PhD
Irreversible inhibitor is specific for a particular type of protease, for example serine proteases, thiol proteases, aspartic proteases and metalloproteases. Common examples of inhibitors include: di-isopropylphosphofluoridate (DFP), phenylmethyl sulphonylfluoride (PMSF) and tosylphenylalanyl-chloromethylketone (TPCK) (all serine protease inhibitors) iodoacetate and cystatin (thiol protease inhibitors) pepstatin (aspartic protease inhibitor) EDTA and 1,10-phenanthroline (metalloprotease inhibitors)
Reversible inhibiton Inhibitor type None Competitive Uncompetitive Mixed Apparent K K, Apparent V max max max max max
Competitive inhibition E+ P EI Competitive inhibitors bind to the enzyme's active site; K is the equilibrium constant for inhibitor binding to E.
max / [S] V max 1 No inhibitor Slope V Tm maX max S mM
Uncompetitive inhibition lo ESI Uncompetitive inhibitors bind at a separate site, but bind only to the ES complex; Ki is the equilibrium constant for inhibitor binding to ES.
Km , = 2 '=1.5 , 1 maX [S] mM
Mixed inhibition ESI Mixed inhibitors bind at a separate site, but may bind to either E or ES.
, maX maX No inhibitor maX [S] mM
Ashish Kr Dwivedi
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