Kinetics of Enzyme Reactions - PowerPoint PPT Presentation

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Kinetics of Enzyme Reactions

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1. The ES complex is in a steady state. 2. All of the enzyme is converted to the ... Toxins: e.g. Amanitin (Amanita phaloides) Diisopropylfluorophosfate (DFP) ... – PowerPoint PPT presentation

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Title: Kinetics of Enzyme Reactions


1
Kinetics of Enzyme Reactions
  • Srbová Martina

2
  • E S ES E P

Rate of the conversion of substrate to products
(S ? P) v kcat ES
3
Michaelis-Menten Equation
1. The ES complex is in a steady state. 2. All of
the enzyme is converted to the ES complex. 3.
Rate of formation of the products will be the
maximum rate possible. Vmax kcatEtotal Turnove
r number number of molecules of substrate that
one molecule of the enzyme can convert to product
per unit time
4
Lineweaver-Burk Plot
  • 1 Km 1 1
  • v Vmax S Vmax

5
Multisubstrate reactions
  • 1. Ternary-complex mechanism

Random mechanism Two substrates A and B can bind
in any order P,Q - products
Ordered mechanism Binding of A is required before
B can bound
6
  • 2. Ping-pong mechanism

Substrate A reacts with E to produce product P
which is released before the second substrate B
will bind to modified enzyme E. The substrate B
is then converted to product Q and the enzyme is
regenerated.
7
Enzyme activity
  • Standard unit of enzyme activity (U) ?mol / min
  • amount of enzyme that convert 1 ?mol substrate
    per 1min
  • SI unit Katal (kat) mol /s
  • - amount of enzyme that convert 1 mol substrate
    per 1s

Factors which effect enzyme activity
temperature optimum for human enzymes is between
35 45 C
pH
8
Reversible Inhibition
9
Competitive Inhibition
Competitive inhibitors bind at substrate binding
site and compete with the substrate for the enzyme
10
Noncompetitive Inhibition
Noncompetive inhibitors bind at a site other than
the substrate binding site
11
Uncompetitive Inhibition
Uncompetitive inhibitors bind only with the ES
form of the enzyme
12
Irreversible Inhibition
  • Irreversible inhibitors cause covalent
    modification of the enzyme
  • Toxins e.g. Amanitin (Amanita phaloides)
  • Diisopropylfluorophosfate (DFP)
  • - binds to the serine in the active site ?
    deactivation of ezyme
  • eg .inhibition of acetylcholine esterase
  • Penicillin inhibits bacterial transpeptidase

13
Control of enzyme activity
  1. Allosteric enzymes

Negative feedback /feedback inhibition
14
  • 2. Covalently modulated enzymes
  • zymogens

Glycogen phosphorylase
undergo cleavage to produce an active enzyme
15
  • Isozymes
  • - catalyze the same reaction
  • - differ in AA sequences, catalytic acitivity
    (substrates/coenzymes affinity..)
  • Lactate dehydrogenase
  • tetrameric, 2 types of subunits M, H
  • M4, M3H, M2H2, MH3, H4
  • Glucokinase x Hexokinase
  • ?Km ?Km
  • liver mostly in the other tissues
  • not inhibited by Glc- 6P inhibited by Glc- 6P

16
Thank you for your attention
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