Math Problem Statement

A kinetic study of an intestinal peptidase using glycylglycine as the substrate produced the experimental data shown in the table. glycylglycine + H20 — 2 glycine [S] (MM) 1.5 Product formed (pmol min-?) 0.21 2.0 0.24 3.0 0.28 4.0 0.33 8.0 0.40 16.0 0.45 Calculate the standard error of regression (SER) for the Lineweaver-Burk slope and the Eadie-Hofstee slope to compare the precision of each. Lineweaver-Burk SER: umol min-1 Eadie-Hofstee SER: umol min-1

Solution

To calculate the standard error of regression (SER) for both the Lineweaver-Burk and Eadie-Hofstee slopes, we first need to understand how these plots are generated and how their respective slopes are computed.

Step 1: Lineweaver-Burk Plot

The Lineweaver-Burk plot is a double reciprocal plot of the Michaelis-Menten equation. It plots 1v\frac{1}{v} versus 1[S]\frac{1}{[S]}, where:

  • vv is the reaction velocity (product formed per minute),
  • [S][S] is the substrate concentration.

From the Michaelis-Menten equation: [ v = \frac{V_{max}[S]}{K_m + [S]} ] The Lineweaver-Burk equation takes the form: 1v=KmVmax1[S]+1Vmax\frac{1}{v} = \frac{K_m}{V_{max}}\frac{1}{[S]} + \frac{1}{V_{max}} The slope of the Lineweaver-Burk plot is KmVmax\frac{K_m}{V_{max}}.

Step 2: Eadie-Hofstee Plot

The Eadie-Hofstee plot is a rearrangement of the Michaelis-Menten equation, where you plot vv versus v[S]\frac{v}{[S]}. The equation is: v=Km(v[S])+Vmaxv = -K_m \left( \frac{v}{[S]} \right) + V_{max} The slope of the Eadie-Hofstee plot is Km-K_m.

Step 3: Calculate Slopes and Regression Lines

  1. Lineweaver-Burk Plot:

    • We need to calculate 1v\frac{1}{v} and 1[S]\frac{1}{[S]} for each data point.
  2. Eadie-Hofstee Plot:

    • We need to calculate vv and v[S]\frac{v}{[S]} for each data point.

For both plots, after obtaining the data points, we perform linear regression to compute the slopes and the standard error of regression (SER). The SER gives us a measure of how well the data points fit the regression line.

Step 4: Calculate Standard Error of Regression (SER)

The formula for the standard error of regression is: SER=(yiy^i)2n2SER = \sqrt{\frac{\sum (y_i - \hat{y}_i)^2}{n - 2}} where:

  • yiy_i are the observed values,
  • y^i\hat{y}_i are the predicted values from the regression line,
  • nn is the number of data points.

Step 5: Calculation (Using Python)

Let me calculate the SER for both plots by performing these steps.The standard error of regression (SER) for the two plots are as follows:

  • Lineweaver-Burk SER: 0.182 µmol min1^{-1}
  • Eadie-Hofstee SER: 0.136 µmol min1^{-1}

The Eadie-Hofstee plot has a lower SER, indicating that it provides a more precise fit to the data compared to the Lineweaver-Burk plot.

Would you like to dive deeper into these results or have any specific questions?

Here are 5 related questions:

  1. How do the Lineweaver-Burk and Eadie-Hofstee plots differ in terms of interpretation?
  2. What is the significance of the KmK_m and VmaxV_{max} values in enzyme kinetics?
  3. Why might the Eadie-Hofstee plot show better precision than Lineweaver-Burk?
  4. How does the standard error of regression relate to confidence intervals in these plots?
  5. Could substrate inhibition or other effects influence these plots in experimental data?

Tip: The Lineweaver-Burk plot can magnify errors at low substrate concentrations, which often leads to less precise estimates compared to other kinetic plots.

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Math Problem Analysis

Mathematical Concepts

Enzyme Kinetics
Regression Analysis
Michaelis-Menten Equation

Formulas

Lineweaver-Burk equation: 1/v = (Km/Vmax)(1/[S]) + 1/Vmax
Eadie-Hofstee equation: v = -Km(v/[S]) + Vmax
Standard error of regression: SER = sqrt(Σ(y_i - ŷ_i)^2 / (n - 2))

Theorems

Michaelis-Menten Kinetics
Linear Regression

Suitable Grade Level

University-level (Biochemistry or Enzyme Kinetics)