Which protein acts as a positive regulator by phosphorylating other proteins when activated?

• A. Ligase
• B. Synthase
• C. Phosphatase
• D. Kinase

Answer: (D)

Verified step by step guidance

1. Understand the role of a kinase: Kinases are enzymes that catalyze the transfer of phosphate groups from high-energy molecules like ATP to specific substrates, a process known as phosphorylation.
2. Recognize the function of phosphorylation: Phosphorylation is a crucial mechanism in cellular signaling and regulation, often activating or deactivating proteins and thus influencing various cellular processes.
3. Differentiate between the given options: Ligase is an enzyme that facilitates the joining of two molecules, Synthase is involved in synthesis reactions, and Phosphatase removes phosphate groups from proteins.
4. Identify the correct option: Kinase is the enzyme that acts as a positive regulator by phosphorylating other proteins, thereby modifying their activity.
5. Conclude the reasoning: Based on the functions of the enzymes listed, Kinase is the correct answer as it is responsible for phosphorylation, a key regulatory mechanism in cells.