Enzymes Have properties shared by all catalysts Enhance the rates of both forward and reverse...
-
date post
20-Dec-2015 -
Category
Documents
-
view
214 -
download
0
Transcript of Enzymes Have properties shared by all catalysts Enhance the rates of both forward and reverse...
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
Enzyme-catalyzed Reactions
ES = Enzyme-substrate complex
formed when substrates fit into the active site of the enzyme
E + S ES E + P
Michaelis-Menten Theory
• vo = initial velocity, ignore reverse reaction, measure rate before P accumulates
• k1 and k-1 represent rapid noncovalent association of substrate with enzyme’s active site
• k2 = rate constant for the chemical conversion of S to P, the rate-limiting step
vo = k2 [ES]
E + S ES E + P k1 k2
k-1
Michaelis-Menten Theory
Assumptions:• vo = initial velocity, ignore reverse reaction• [ES] is constant• Conversion of S to P is rate-limiting, vo = k2 [ES]
E + S ES E + P k1 k2
k-1
Vmax [S]Vo = -------------
Km + [S]
Km = Michaelis constant
Is a measure of the affinity of E for S
k-1 + k2
Km = k1
Inverse relationship: when Km is small affinity is great
€
kcat = catalytic constant or turnover number
Moles of S converted to P per second per mole of enzyme ( or active site)
Inverse of kcat tells you how much time is required to convert one mole S to P
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
Consider inhibitors first reversible or irreversible inhibition
noncovalent vs. covalent interactions between E and I