Question

Which of the following is a FALSE statement about adenylylation of Glutamine synthetase?

A. At high ammonia, a small amount of ATP is used to deactivate the enzyme, thus saving a large amount of ATP that would otherwise be required to data catalyze the synthesis of many molecules of glutamine.

B. The process allows available ammonia/ammonium-ion to be used in place of a glutamine in biosynthetic reactions that otherwise require glutamine.

C. The extent of PII uridylylation controls the extent of glutamine synthetase adenylylation.

D. High glutamine favors deadenylylations of GS-AMP, the active form of this bacterial enzyme.

E. In GS-AMP, the covalently bound AMP blocks substrate access to the active site of glutamine synthetase.

Answer 1

Answer:-

A) Basically, it should be considered as AMP or ADP as inhibitors of this enzymatic activity which in turn binds to the active site to complete with glutamate and thus inhibition is achieved. ATP is associated with activation only when Ammonia is stated to be present on the upper plane of the active site whereas ATP binding occurs on lower plane and both are essential in enzymatic activity. No negative feedback is associated with presence of enzyme adenylyltransferase which required UMP for deadenylation however in case of adenylation ATP is being converted to AMP in order to make the enzyme inactive. So, inhibition depends on presence of endproducts as mentioned above but can be stated to form by dissociation of ATP associated with UMP removal followed by adenylation. So, option A is true.

B) Ammonia and ammonium ions has two purposes in the two step reaction. In the second step, it is ammonium ion that binds to the active site which in turn is most essential for binding to the intermediate involved in conversion of glutamate to Glutamine. It is indeed part of the process and cannot be used as substitute for Glutamine and hence option B is FALSE.

C) Basically uridylation of P_II is associated with addition of uridine residues which is associated with deadenylation as it removes the inhibitory AMP active site binding thereby accessing the progression to form the active form of enzyme. The extent to which uridylation occurs will not determine the adenylation of Glutamine synthetase as both the processes are oppositely related. Hence, option C is FALSE.

D) Accordingly, more the content of Glutamine, more enhanced will be the process of uridinylation as UMP will not be built up in association with the Adenylyltransferase and hence there would be inhibition. Glutamine along with Pi will act to inhibit the enzyme activity and thereby the entire mechanism. So, option D is True.