Which of the following is an example of non-competitive and reversible type inhibition?

Options

A. CN poisoning of cytochrome oxidase
B. Inhibition of hexokinase by glucose-6P
C. Inhibition of succinic dehydrogenase by malonate
D. (1) and (3) both

Answer

To determine which of the given options represents an example of non-competitive and reversible type inhibition, we can analyze each option step-by-step.

### Step 1: Understand Non-Competitive Inhibition
Non-competitive inhibition occurs when an inhibitor binds to an enzyme at a site other than the active site, which prevents the enzyme from functioning effectively regardless of the substrate concentration. This type of inhibition is reversible, meaning that the inhibitor can dissociate from the enzyme, allowing the enzyme to regain its activity.

### Step 2: Analyze the Options
1. **Cyanide poisoning of cytochrome c-oxidase**: Cyanide binds irreversibly to cytochrome c-oxidase, leading to permanent inhibition. This is not an example of reversible inhibition.

2. **Inhibition of hexokinase by glucose 6-phosphate**: Glucose 6-phosphate acts as a non-competitive inhibitor of hexokinase. This inhibition is reversible, as the inhibitor can dissociate from the enzyme.

3. **Inhibition of succinic dehydrogenase by melanoid**: This type of inhibition is competitive rather than non-competitive. The inhibitor competes with the substrate for the active site, which does not fit the criteria for non-competitive inhibition.

4. **First and third both**: Since the first option (cyanide poisoning) is irreversible and the third option (inhibition by melanoid) is competitive, this option is incorrect.

### Step 3: Conclusion
Based on the analysis, the correct answer is **inhibition of hexokinase by glucose 6-phosphate**, as it is an example of non-competitive and reversible inhibition.

### Final Answer
**Inhibition of hexokinase by glucose 6-phosphate** is an example of non-competitive and reversible type inhibition.

---