Which one of the following is not protein?

Options

A. Myosin
B. Actin
C. Albumin
D. Haematin.

Answer

To determine which of the following options is not a protein, we will analyze each option provided:

1. **Myosin**:
- Myosin is a type of contractile protein found in muscle tissue. It plays a crucial role in muscle contraction. Therefore, myosin is a protein.

2. **Actin**:
- Actin is another contractile protein that works alongside myosin in muscle contraction. It is also found in muscle cells and is essential for various cellular functions. Thus, actin is also a protein.

3. **Albumin**:
- Albumin is a well-known protein that is found in egg whites (the albumen) and in blood plasma. It plays important roles in maintaining osmotic pressure and transporting various substances in the blood. Therefore, albumin is a protein.

4. **Hematin**:
- Hematin is a compound that is derived from the oxidation of heme, which is part of hemoglobin. Hematin itself is not a protein; it is a pigment that is involved in various biochemical processes, including the synthesis of globulin. Thus, hematin is not a protein.

Based on this analysis, the correct answer to the question "Which one of the following is not a protein?" is **Hematin** (option D).

### Step-by-Step Solution:
1. Identify and analyze each option provided.
2. Determine whether each option is a protein or not.
3. Conclude that myosin, actin, and albumin are proteins.
4. Identify hematin as the compound that is not a protein.
5. State the final answer: Hematin (option D) is not a protein.