Question:

Which of the following is a phospho-protein?

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Conjugated Proteins:
Phosphoprotein = Casein, Vitellin.
Glycoprotein = Immunoglobulins, Mucin.
Lipoprotein = Chylomicrons, VLDL, LDL.
  • Immunoglobulin G
  • Albumin
  • Casein
  • Beta-lipoprotein
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The Correct Option is C

Solution and Explanation


Step 1: Understanding the Concept:

Conjugated proteins contain non-protein prosthetic groups (phosphate, carbohydrate, lipid, or heme) covalently attached to the polypeptide chain.

Step 2: Detailed Explanation:

Evaluating the conjugated proteins:
1. Casein: The major phosphoprotein of milk (constituting $\approx 80\%$ of bovine milk protein), containing serine and threonine residues post-translationally esterified with phosphate groups (forming phosphoserine clusters that chelate calcium as calcium caseinate micellar complexes).
2. Immunoglobulin G: Glycoprotein.
3. Albumin: Simple globular protein.
4. Beta-lipoprotein: Conjugated lipid-protein complex.

Step 3: Final Answer:

Hence, Casein is a phospho-protein, corresponding to option (C).
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