[Judy]

Which statement is FALSE regarding regulation of the pyruvate dehydrogenase complex?
A) In E. coli, a high ratio of [NAD+]/[NADH] activates the complex.
B) In E. coli, high levels of ATP enhance the activity of pyruvate dehydrogenase kinase.
C) In plants, NH4+ inhibits the complex by enhancing the activity of pyruvate dehydrogenase kinase.
D) In mammals, both fatty acids and acetyl-CoA inhibit the complex.
E) In skeletal muscle, both NAD+ and Ca2+ activate the complex.

The answer is B.

Is there a hint of why C is correct? Thanks

[Babcock_Hall]

Would you please provide your thoughts first?  That is a Forum Rule (see red link above).

[Judy]

Would you please provide your thoughts first?  That is a Forum Rule (see red link above).

NH4+ is able to stimulate PDH kinase, as such it regulates the PDH complex?

[Babcock_Hall]

By the name "kinase," what can you reasonably infer about the substrates for this enzyme?  Do you know how reversible covalent modification is used to regulate the liver isozyme of pyruvate kinase?  You can apply the same principles in this example.

[Judy]

By the name "kinase," what can you reasonably infer about the substrates for this enzyme?  Do you know how reversible covalent modification is used to regulate the liver isozyme of pyruvate kinase?  You can apply the same principles in this example.

Kinase means to perform phosphorylation on enzymes. As per pyruvate kinase, it also utilizes phosphorylation to inactivate itself and so does PDH complex.

I think I got it, thanks a lot.

[Babcock_Hall]

Pyruvate kinase does not autophosphorylate; the reaction is performed by protein kinase A. The PDH complex needs one enzyme to phosphorylate it.  Both PK and the PDH complex also need phosphoprotein phosphatases to remove this phosphoryl group using water, but that is not part of the present question.