The synthesis of 5-phosphoribosylamine from PRPP is
(I)inhibited allosterically by ATP and GTP.
(II)activated by PRPP via feed forward activation.
(III)controlled by cAMP dependent phosphorylation.
A)I,II,III,
B)I,II
C)II,III
D)II only
E)III only

Question

Quizplus · Accepted Answer

The statement (I) is correct because the synthesis of 5-phosphoribosylamine is inhibited allosterically by ATP and GTP. They act as negative effectors and inhibit the activity of the enzyme. 
The statement (II) is also correct because the synthesis of 5-phosphoribosylamine is activated by PRPP via feed forward activation. PRPP is a substrate of the enzyme and also acts as a positive effector, increasing the activity of the enzyme. 
However, the statement (III) is not correct because there is no evidence that the synthesis of 5-phosphoribosylamine is controlled by cAMP-dependent phosphorylation. Therefore, the answer is B, which includes only the correct statements (I) and (II).

The Synthesis of 5-Phosphoribosylamine from PRPP Is