Q.53 The relationship between log(MW) [where MW – molecular weight in kDa] of a mixture of protein standards and their retention factors (Rf) obtained from native-PAGE is log₁₀(MW) = −2Rf + 3. If the measured retention factor for a protein with 180 amino acids is 0.5, then the number of identical monomers in the protein is _______.

The relationship log₁₀(MW) = −2Rf + 3 from native-PAGE standards gives the native molecular weight (MW) of the oligomeric protein, while the 180 amino acids indicate the monomer size. Substituting Rf = 0.5 yields MW = 100 kDa for the native protein; the monomer MW ≈ 19.8 kDa (180 × 110 Da/aa), so the protein consists of 5 identical monomers. Native-PAGE preserves oligomeric state, enabling subunit count via MW ratio.

Problem Breakdown

The equation log₁₀(MW) = −2Rf + 3 relates log molecular weight (kDa) to retention factor (Rf = migration distance/protein front) for standards in native-PAGE. For Rf = 0.5: log₁₀(MW) = −2(0.5) + 3 = 2, so MW = 10² = 100 kDa—this is the native (oligomeric) MW. Monomer MW uses average amino acid residue mass of ~110 Da: 180 aa × 110 Da/aa = 19,800 Da = 19.8 kDa. Number of identical monomers = 100 / 19.8 ≈ 5.

Native-PAGE Principles

Native-PAGE separates proteins by charge/mass/shape without denaturants, retaining oligomers unlike SDS-PAGE. Standards create linear log(MW) vs. Rf plots (R² > 0.99 ideal); unknown Rf interpolates native MW. For oligomers, this reveals subunit count when monomer size is known from sequence.

Calculation Steps

1. Compute native MW: log₁₀(MW) = −2(0.5) + 3 = 2 → MW = 100 kDa .

2. Estimate monomer MW: 180 aa × 110 Da/aa ÷ 1000 = 19.8 kDa.

3. Oligomer number: 100 ÷ 19.8 = 5 (integer, as identical monomers).

No options provided; fill-in answer is 5. Approximation (20 kDa monomer) confirms 100/20 = 5.

Introduction to Log(MW) Native-PAGE Rf Protein Monomers 180 Amino Acids

Determining protein oligomeric state via log(MW) native-PAGE Rf is key for CSIR NET Life Sciences, revealing how many identical monomers form native complexes. This guide solves: given log₁₀(MW in kDa) = −2Rf + 3 and Rf = 0.5 for a protein with 180 amino acids, find the oligomer number. Native-PAGE migration (Rf) estimates native MW from standards, compared to monomer size (~110 Da/aa average).

Why Native-PAGE for Oligomer Analysis

Native-PAGE keeps quaternary structure intact, plotting log(MW) vs. Rf linearly for globular proteins. Unlike SDS-PAGE (denatures to monomers), it shows true MW for oligomers. For CSIR NET, recognize: Rf decrease with larger MW due to sieving.

Step-by-Step Solution: 180 Amino Acids Protein

• Native MW from Rf: log₁₀(MW) = −2(0.5) + 3 = 2 → MW = 100 kDa.

• Monomer MW: 180 × 110 Da = 19.8 kDa (divide by 1000 for kDa).

• Monomers: 100 / 19.8 = 5.

CSIR NET Tips and Variations

Use ~110 Da/aa for quick estimates (exact varies by sequence). If Rf differed (e.g., 0.6: MW ≈ 39.8 kDa → ~2 monomers), recalculate similarly. Practice with standards for linearity.