Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
The molar extinction coefficients of Trp and Tyr at 280 nm are 5690 and 1280 M-1.cm-1,
respectively. The polypeptide chain of yeast alcohol dehydrogenase (37 kDa) contains 5 Trp and 14
Tyr residues. The absorbance at 280 nm of a 0.32 mg.mL-1 solution of yeast alcohol dehydrogenase
measured in a cuvette of 1 cm pathlength will be ________________.
(Assume that the molar extinction coefficient values for Trp and Tyr apply to these amino acids in
the yeast alcohol dehydrogenase).
Official Answer Key:
0.37 - 0.43
Step-by-Step Solution & Explanation
### **Step-by-Step Solution & Mathematical Derivation (GATE BT 2016 Q.53)**
**1. Governing Concept & Definition**:
- **Topic**: Biophysical Chemistry & Protein Extinction Coefficient
- By Gill and von Hippel's method, the total molar extinction coefficient ($\epsilon_{280}$) of a native protein is:
$\epsilon_{280} = n_{\text{Trp}} \cdot \epsilon_{\text{Trp}} + n_{\text{Tyr}} \cdot \epsilon_{\text{Tyr}} + n_{\text{Cys}} \cdot \epsilon_{\text{Cys}}$
**2. Detailed Step-by-Step Calculation**:
- Calculating total absorbance for given molar concentration and cuvette path length yields:
$A_{280} = 0.40$
**3. Final Answer**:
- **Calculated Value**: **0.40**
- **Official GATE Accepted Range**: **0.37 to 0.43**
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.