June 18, 2021, 11:24:21 PM
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Topic: Regarding regulation of the pyruvate dehydrogenase complex  (Read 264 times)

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Offline Judy

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Regarding regulation of the pyruvate dehydrogenase complex
« on: April 19, 2021, 07:32:43 AM »
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

Offline Babcock_Hall

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Re: Regarding regulation of the pyruvate dehydrogenase complex
« Reply #1 on: April 19, 2021, 11:48:03 AM »
Would you please provide your thoughts first?  That is a Forum Rule (see red link above).

Offline Judy

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Re: Regarding regulation of the pyruvate dehydrogenase complex
« Reply #2 on: April 20, 2021, 02:29:25 AM »
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?

Offline Babcock_Hall

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Re: Regarding regulation of the pyruvate dehydrogenase complex
« Reply #3 on: April 20, 2021, 08:20:26 AM »
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.

Offline Judy

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Re: Regarding regulation of the pyruvate dehydrogenase complex
« Reply #4 on: April 20, 2021, 08:52:04 AM »
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.

Offline Babcock_Hall

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Re: Regarding regulation of the pyruvate dehydrogenase complex
« Reply #5 on: April 20, 2021, 09:27:17 AM »
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.

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