Question

Which enzyme is responsible for the conversion of protopectin to soluble pectin, leading to fruit softening?

• A. Amylase
• B. Protopectinase
• C. Lipoxygenase
• D. Peroxidase

Hint:

To identify the enzyme, look at the substrate: Protopectin is converted to soluble pectin by the enzyme Protopectin-ase. Subsequent pectin depolymerization is performed by pectin methylesterases and polygalacturonases.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the specific enzyme responsible for solubilizing insoluble protopectin into soluble pectin, which weakens the middle lamella and causes fruits to soften during ripening.

Step 2: Detailed Explanation:

• Role of Pectin in Fruit Structure: The middle lamella and primary cell walls of unripe fruit cells contain high amounts of insoluble pectic substances, primarily protopectin, which binds cells together and gives unripe fruits their firm, hard texture.
Protopectin to Pectin Solubilization:

• During ripening, physiological changes activate cell-wall hydrolyzing enzymes.

• Protopectinase is the enzyme that specifically hydrolyzes insoluble protopectin, releasing water-soluble pectin.

• This solubilization weakens the adhesive bonds between adjacent cells, allowing cells to slide past one another, which leads to the characteristic softening of fruit tissues.

• Other Enzymes:

• Amylase: Hydrolyzes starch into sugars, increasing sweetness during ripening but not directly driving structural softening.

• Lipoxygenase: Catalyzes the oxidation of polyunsaturated fatty acids, contributing to flavor/aroma changes or oxidative rancidity.

• Peroxidase: Involved in electron-transfer and active-oxygen metabolism, often associated with tissue browning or stress responses.

Step 3: Final Answer:
The enzyme responsible for converting protopectin into soluble pectin is protopectinase, corresponding to option (B).