lecture 6-Notes on Enzyme Activity Practical

Overview of Enzyme Activity Practical

Focus on the practical implications of enzyme biochemistry through trypsin and BAPNA interactions, emphasizing the understanding of enzyme kinetics and the methodologies used in enzymology, which are crucial for applications in biochemistry and molecular biology.

Resources and Course Structure

Lectures: Recorded on Panopto, accessible via Brightspace. Students are encouraged to review recorded lectures to reinforce their understanding and prepare for quizzes.

Topics: Organized by week, covering essential aspects of enzymatic reactions, mechanisms, and kinetics with details on Home Page for easy navigation.

MCQs: Available post-lecture, designed to assess comprehension of key concepts discussed in class, allowing students to gauge their understanding of the material.

Lecture Slides:

  • Important words: Blue font to highlight essential terminology.

  • Definitions: Dark red font to denote key concepts crucial for student comprehension.

  • Equations: Green font to distinguish mathematical representations.

Enzyme Basics

Proteases: Enzymes that catalyze the hydrolytic cleavage of peptide bonds, playing vital roles in various physiological processes including digestion and protein turnover.

Trypsin: A specific type of serine protease that hydrolyzes peptide bonds at the carbonyl groups of positively charged amino acids such as lysine (Lys) or arginine (Arg), critical for its role in the digestive system and protein metabolism.

Artificial Substrate: BAPNA

  • Definition: Nα-Benzoyl-DL-arginine p-nitroanilide, a synthetic substrate employed in determining protease activity.

  • Use in Enzyme Studies:

    • Serves as an artificial substrate for studying trypsin's activity due to its specificity; upon hydrolysis, it releases p-nitroaniline, which can be quantified spectrophotometrically.

  • Hydrolysis equation:
    BAPNA+H2O→Nα-Benzoyl-DL-arginine+p-nitroanilide\text{BAPNA} + \text{H}_2\text{O} \rightarrow \text{Nα-Benzoyl-DL-arginine} + \text{p-nitroanilide}

Spectrophotometry

Definition: Measurement of absorbance and emission of light by matter, a crucial technique in biochemical analysis that allows for the quantification of substances based on their optical properties.

Absorbance Equation:
A=log⁡10(I0/I)A = \log{10}(I_0/I)
Where:

  • $I_0$: Intensity of incident light

  • $I$: Intensity of emergent light, providing a basis for quantifying sample concentrations.

Practice Calculating Absorbance

  1. 90% Light Absorption:
    A=log⁡10(100/10)=1A = \log_{10}(100/10) = 1

  2. 50% Light Absorption:
    A=log⁡10(100/50)=0.301A = \log_{10}(100/50) = 0.301

  3. 10% Light Absorption:
    A=log⁡10(100/90)=0.046A = \log_{10}(100/90) = 0.046

Beer-Lambert Law

Core Principle: Absorbance relates to solute concentration and light path length, providing a linear relationship that is instrumental in quantitative spectrophotometry.

Formula:
log⁡10(I0/I)=ε×d×[C]\log{10}(I_0/I) = \varepsilon \times d \times [C]
Where:

  • $\varepsilon$: Absorption coefficient, specific to each substance.

  • $d$: Light path length, typically in cm.

  • $[C]$: Concentration of solute in solution.

  • From the equation, absorbance $A$ can also be expressed as:
    A=ε×d×[C]A = \varepsilon \times d \times [C]

Task 1: Effect of Enzyme Concentration

Procedure:

  • Keep substrate concentration (BAPNA) constant while adjusting trypsin concentration to explore the relationship between enzyme concentration and reaction rate.

Turnover Number (kcat):

  • Concept derived from Michaelis-Menten kinetics, defined as the maximum number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is saturated with substrate.

Calculating Absorbance Change

Measure change in absorbance per minute ($\Delta A/min$) for samples, reflecting the rate of reaction.
Convert to molar product concentration using:
ΔA/min=ε×Δ[C]/min\Delta A/min = \varepsilon \times \Delta [C]/min
Rearranging gives:
Δ[C]/min=ΔA/min/ε\Delta [C]/min = \Delta A/min / \varepsilon

Practical Concentration Conversion

Convert concentration from mol/L to µmol/L:
1 mol/L=1×106 µmol/L1 \text{ mol/L} = 1 \times 10^6 \text{ µmol/L}

Example Calculations

Change in concentration per minute for each cuvette:

  • Examples provided for various absorbance results leading to rates, which help in understanding how concentration changes affect overall enzyme activity.

Task 2: Effect of Substrate Concentration

Variables:

  • Keep enzyme concentration constant, increase substrate (BAPNA) to examine the enzyme's kinetic response as substrate availability changes.

Michaelis Constant (km):

  • Indicates enzyme affinity for substrate; a low km indicates high affinity, which plays a crucial role in determining reaction efficiency.

Calculate Concentrations:

  • Stock concentration: 0.1% (w/v)=1.0g/L0.1\%\text{ (w/v)} = 1.0 g/L

  • Molar concentration using molecular weight of BAPNA, calculating effective concentrations necessary for experimental setups.

Experimental Data Processing

Use Beer-Lambert Law for absorbance changes, converting values to appropriate units for meaningful data analysis and interpretation.

Final Graphing and Analysis

Plotting reaction rates against substrate concentrations leads to insights about enzyme kinetics, allowing for graphical estimation of the Michaelis constant and assessment of enzyme efficiency under varying conditions.

Miscellaneous Problem-Solving and MCQs

Practice problems provided to reinforce understanding of concepts like Beer-Lambert Law and enzyme kinetics, strengthening knowledge through application.

Multiple choice questions aim to solidify key definitions and principles surrounding enzyme activity, enhancing retention and comprehension for practical applications in laboratory settings.

Key Takeaways:

  • Understand the effect of enzyme concentration on reaction rates and substrate concentration implications on enzyme kinetics, which are essential for advancements in biochemistry, pharmaceuticals, and environmental science.