Which of the following is not true of ATP into cAMP ?

Options

A. It is a second messenger
B. The enzyme adenylate cyclase converts ATP into `cAMP`
C. In the mechanism of a protein hormone, `cAMP` is involved
D. None

Answer

To determine which statement is not true regarding the conversion of ATP into cAMP, we can analyze each option systematically.

### Step-by-Step Solution:

1. **Understanding ATP and cAMP**:
- ATP (adenosine triphosphate) is a molecule that stores and transfers energy within cells.
- cAMP (cyclic adenosine monophosphate) is a derivative of ATP and acts as a secondary messenger in various biological processes.

2. **Evaluating Statement 1**: "cAMP is a second messenger."
- This statement is true. cAMP functions as a secondary messenger that transmits signals from hormones and other signaling molecules that cannot enter the cell.

3. **Evaluating Statement 2**: "The enzyme adenylate cyclase converts ATP into cAMP."
- This statement is also true. Adenylate cyclase is the enzyme responsible for catalyzing the conversion of ATP to cAMP.

4. **Evaluating Statement 3**: "In the mechanism of protein hormone, cyclic AMP is involved."
- This statement is correct as well. cAMP plays a crucial role in the signaling pathways of protein hormones, acting as a secondary messenger to relay the signal inside the cell.

5. **Evaluating Statement 4**: "None of the above statements are incorrect."
- Since the first three statements are true, this statement is also correct. Therefore, there is no statement among the first three that is false.

### Conclusion:
Since all the first three statements about ATP conversion into cAMP are true, the answer to the question "Which of the following is not true of ATP into cAMP?" is that none of the first three statements are incorrect.

### Final Answer:
None of the statements are incorrect.