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Monday, 8 January 2018

Factors affecting enzymes activity

Factors affecting enzymes activity

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 Factors affecting enzymes activity:

  • Substrate concentration
  • Enzyme concentration
  • pH
  • Temperature
 How enzyme activity measured ?
  1. Decrease in substrate concentration
  2. Increase in product concentration
  3. Reaction velocity is the amount of substrate converted in to product per time
  4. Increase in substrate concentration leads to increase in the velocity of reaction .
  • At Vmax increase in the amount of substrate causes no increase in the velocity of the reaction .
Michaelis constant (Km ) :is the substrate concentration at half maximum velocity
  • It measures the enzyme affinity to substrate
  • Low Km means  high affinity to substrate
  • High Km mean  low affinity to substrate

Lineweaver-Burk plot

  • To calculate the Vmax
  • To calculate the Km
  • To determine the type of inhibitor
  • Increase in the enzyme concentration leads to increase in the velocity of reaction
Optimal pH : 
  • the pH at which enzyme acts maximally .
  • Above or below this pH the rate of reaction will decreased .
  • Each enzyme has its own pH.


  • The reaction velocity increases with the temperature until a peak velocity is reached .
  • Further increase in temperature decrease reaction velocity as a result of denaturation.
  • Most enzymes are denatured at 55-60  .

Inhibitors of enzymes:

  • Competitive Inhibitors
  • Non competitive Inhibitors

Enzymes regulation

  • Why are enzymes regulated?

The biochemical reactions in the body found as a pathways. Cells do not need all activities at one time . So each pathway has its own regulatory enzyme(s)

Regulation of enzymes:

  • Feedback inhibition
  • Covalent modification : adding or removal of phosphate

Allosteric enzymes

Have another site in addition to the active site . The other site binds to modulators. Modulator may be positive or negative . 
Compartmentalization Enzymes found in cellular sub-compartments such as lysosomes or mitochondria and are only active there Control of synthesis and degradation : 
  1. Constitutive enzymes (continuous synthesis)
  2. Adaptive enzymes (on demand)

Zymogens : (inactive enzymes) the active site is covered by a peptide mask.

Isozymes : are more than one enzyme catalyze the same reaction.

Clinical importance of isoenzymes:

  • diagnosis of some diseases  eg:
  • LDH1 important in heart disease (myocardial infarction)
  • LDH5 important in liver diseases

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