Enzyme Kinetics Notes

Learning Objectives

  • Understanding how to transform data to plot a Lineweaver-Burk graph to calculate Vmax and Km.
  • Using Vmax and Km values to determine the natural substrate for an enzyme, which relates to enzyme efficiency for a substrate.

Initial Rate Measurement

  • Initial Rate (vo): The rate of the reaction measured at the beginning, closely associated with substrate concentrations.
  • Plotting vo against various substrate concentrations at constant enzyme concentration results in a saturation curve.

Concepts of Enzyme Kinetics

  • Saturation Curve: As substrate concentration increases, the reaction rate (vo) approaches a maximum value, termed Vmax, due to enzyme saturation.

Calculating Km and Vmax

  • Initial reaction rates (ΔP/Δt) are measured in units of concentration over time (e.g., M.s-1 or mol.s-1).
  • Commonly, values of vo and [Substrate] are plotted to form a Michaelis-Menten curve.
Lineweaver-Burk Plot
  • The Lineweaver-Burk plot inverts the Michaelis-Menten equation:
    1v<em>0=K</em>mV<em>max+1V</em>max(1[S])\frac{1}{v<em>0} = \frac{K</em>m}{V<em>{max}} + \frac{1}{V</em>{max}} \left( \frac{1}{[S]} \right).
  • Lineweaver-Burk Characteristics:
    • Y-intercept: 1Vmax\frac{1}{V_{max}}
    • Slope: K<em>mV</em>max\frac{K<em>m}{V</em>{max}}
    • X-intercept: −1Km-\frac{1}{K_m}

Saturation of Enzymes

  • The saturation of an enzyme by substrate can be described:
    v<em>0V</em>max=[S]Km+[S]\frac{v<em>0}{V</em>{max}} = \frac{[S]}{K_m + [S]}
  • Understanding how changes in substrate concentration range affects the percentage saturation of the enzyme.

Applications of Vmax and Km

  • Knowledge of Vmax and Km allows determination of an enzyme's physiological substrate, which is pivotal in drug design and development.

Example Calculation

  • For glucose and fructose:
    • Glucose:
    • Km = 1×10−5 M1 \times 10^{-5} \, M, Physiological Conc. = 1×10−5 M1 \times 10^{-5} \, M
    • Result: 50% of hexokinase has glucose bound.
    • Fructose:
    • Km = 1×10−3 M1 \times 10^{-3} \, M, Physiological Conc. = 1×10−6 M1 \times 10^{-6} \, M
    • Result: 0.001% of hexokinase has fructose bound.

Efficiency Assessment

  • Ratio of Vmax/Km for glucose is approximately 100 times higher than for fructose, indicating that glucose is phosphorylated more efficiently by hexokinase than fructose.

Key Takeaways

  1. Understanding terms vo, Vmax, and Km.
  2. Calculating these values through graphical analysis.
  3. Implications of these calculations in physiological processes and disease states, such as type 2 diabetes.

Further Study

  • Additional workshops will cover calculations related to enzyme kinetics, including activities related to hexokinase mutations and their association with diabetes.