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Renin Angiotensin Mechanism.

Lineweaver–Burk Plot.

 

Introduction:

  • Enzymes are the organic biological catalysts, which speed up the rate of biochemical reactions without undergoing any change.

  • They are specific to one type of reaction and one, or a small number of, closely related reactants known as substrates. 

  • Enzyme kinetics is the study of enzyme reaction rates and the conditions which affect them. 

  • In this lecture, we will discuss the Lineweaver–Burk Plot which gives us important information regarding the enzyme inhibition.

Lineweaver–Burk Plot.

  • Since, Vmax is achieved at infinite substrate concentration, it is impossible to estimate Vmax and hence Km from a hyperbolic plot.

  • To overcome this difficulty, the Michaelis–Menten equation was transformed into an equation for a straight line by Lineweaver and Burk.

  • The Lineweaver–Burk plot (or double reciprocal plot) is a graphical representation of the Lineweaver–Burk equation of enzyme kinetics, described by Hans Lineweaver and Dean Burk in 1934.

  • This plot is a derivation of the Michaelis–Menten equation and is represented as:

  • Where,

    • V is the reaction velocity (the reaction rate), 

    • Km is the Michaelis–Menten constant, 

    • Vmax is the maximum reaction velocity,

    • [S] is the substrate concentration.

  • It gives a straight line, with the intercept on the y-axis equal to 1/Vmax, and the intercept on the x-axis equal to Km/Vmax. The slope of the line is equal to Km/Vmax.

  • Vmax and Km can be determined experimentally by measuring V0 at different substrate concentrations. Then a double reciprocal or Lineweaver–Burk plot of 1/V0 against 1/[S] is made.

  • Reversible enzyme inhibitors can be classified as either competitive or noncompetitive, and can be distinguished easily via a Lineweaver–Burk plot.

  • It is a useful way of determining how an inhibitor binds to an enzyme.

  • Competitive inhibition can be recognized by using a Lineweaver–Burk plot if V0 is measured at different substrate concentrations in the presence of a fixed concentration of inhibitor.

  • A competitive inhibitor increases the slope of the line on the Lineweaver–Burk plot, and alters the intercept on the x-axis (since Km is increased), but leaves the intercept on the y- axis unchanged (since Vmax remains constant).

  • Noncompetitive inhibition can also be recognized on a Lineweaver–Burk plot since it increases the slope of the experimental line, and alters the intercept on the y-axis (since Vmax is decreased), but leaves the intercept on the x-axis unchanged (since Km remains constant).

Uses:

  1. Used to determine important terms in enzyme kinetics, such as Kmand Vmax (Before use of advanced computers).

  2. Provides a quick, information of the different forms of enzyme inhibition from the plot.

Commonly Asked Questions.

  1. Explain Lineweaver–Burk Plot and give its uses.
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