Which of the following is a marker enzyme for the Lysosome?
1. Acid phosphatase
2. Signal peptidase
3. Succinate dehydrogenase
4. Lactate dehydrogenase

Introduction to Lysosomes and Marker Enzymes

Lysosomes are membrane-bound organelles found in eukaryotic cells that play a critical role in the degradation and recycling of cellular waste. These organelles contain hydrolytic enzymes that break down biomolecules such as proteins, nucleic acids, lipids, and carbohydrates. Identifying lysosomes within a cell is often accomplished using marker enzymes. One of the most well-known and widely used marker enzymes for lysosomes is acid phosphatase. In this article, we will explore the role of acid phosphatase, its significance as a lysosomal marker enzyme, and why it is essential for cellular function.

Key Phrase: Marker Enzyme for Lysosome

✅ Question and Answer

Question:
Which of the following is a marker enzyme for the lysosome?

Options:

1. Acid phosphatase
2. Signal peptidase
3. Succinate dehydrogenase
4. Lactate dehydrogenase

Correct Answer:
✔️ Option 1: Acid phosphatase

What are Lysosomes?

Lysosomes are small, spherical organelles present in the cytoplasm of animal cells. They are often referred to as the “cell’s recycling center” due to their ability to break down cellular waste and damaged organelles. Lysosomes are rich in hydrolytic enzymes, including:

• Proteases
• Lipases
• Nucleases
• Carbohydrases

These enzymes are active at an acidic pH (around 4.5 to 5.0), which is maintained by proton pumps located on the lysosomal membrane.

What is a Marker Enzyme?

A marker enzyme is a specific enzyme that is highly enriched in a particular organelle. Its presence serves as a biochemical indicator for the identification and isolation of that organelle.

Characteristics of Marker Enzymes:

Highly enriched in the specific organelle.
Essential for organelle-specific functions.
 Used for cellular fractionation and biochemical analysis.

Why Acid Phosphatase is the Marker Enzyme for Lysosomes

1. High Concentration in Lysosomes

• Acid phosphatase is one of the most abundant enzymes in lysosomes.
• It catalyzes the hydrolysis of phosphate esters at an acidic pH.

2. Localized Activity

• Acid phosphatase activity is localized to lysosomes, making it a reliable marker for isolating and identifying lysosomes.

3. Diagnostic Tool

• The presence of acid phosphatase is often used as a diagnostic tool to study lysosomal function and detect lysosomal storage diseases.

How Acid Phosphatase Works

The enzyme acid phosphatase functions by breaking down phosphate esters into inorganic phosphate and alcohol under acidic conditions.

Reaction:

​R-O-PO32−​+H2​O→R-OH+H3​PO4​

Where:

• R-O-PO3²⁻ = Phosphate ester
• R-OH = Alcohol
• H₃PO₄ = Phosphoric acid

Comparison of Marker Enzymes for Other Organelles

Why Option 1 (Acid Phosphatase) is Correct

• Acid phosphatase is highly localized to lysosomes.
• Its hydrolytic activity at acidic pH makes it a functional marker for lysosomes.
• Therefore, acid phosphatase is the correct answer.

Why Other Options Are Incorrect

Signal Peptidase – Found in the endoplasmic reticulum, involved in protein processing.
Succinate Dehydrogenase – Present in mitochondria, involved in the Krebs cycle and electron transport chain.
Lactate Dehydrogenase – Found in the cytoplasm, involved in anaerobic glycolysis.

Functions of Acid Phosphatase in Lysosomes

1. Autophagy – Degrades damaged organelles and proteins.
2. Phagocytosis – Breaks down pathogens engulfed by immune cells.
3. Endocytosis – Processes and recycles extracellular material.
4. Cell Signaling – Regulates cellular response to stress and damage.

Clinical Significance of Acid Phosphatase

Lysosomal Storage Diseases

Deficiency of acid phosphatase leads to the accumulation of undigested substrates in lysosomes, causing lysosomal storage diseases such as:

• Pompe disease – Deficiency in acid α-glucosidase.
• Gaucher disease – Deficiency in glucocerebrosidase.

Cancer Diagnosis

Elevated levels of acid phosphatase are used as a biomarker for diagnosing prostate cancer and other malignancies.

Bone Metabolism

Acid phosphatase is involved in bone resorption, making it a marker for osteoclast activity.

Importance of Understanding Lysosomes for Competitive Exams

Knowledge of lysosomes and their functions is essential for success in:
CSIR NET Life Science
DBT BET JRF
IIT JAM
GATE Biotechnology

Conclusion

The correct answer to the question is Option 1 – Acid Phosphatase. Acid phosphatase is widely used as a marker enzyme for lysosomes due to its high localization and enzymatic activity under acidic conditions. Understanding the role of lysosomes and their marker enzymes is essential for mastering cell biology and acing competitive exams like CSIR NET Life Science, DBT BET JRF, IIT JAM, and GATE Biotechnology.

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