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  #1  
Old 07-22-2012
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Biochemistry 20 Raw Eggs a Day!

A 25-year-old man eats 20 raw eggs a day to increase protein for his bodybuilding routine. This unusual diet affects the activity of which of the following enzymes?

a) Acetyl-CoA carboxylase
b) Acyl-CoA dehydrogenase
c) Fatty acid synthase
d) Fatty acid thiokinase
d) Propionyl-CoA carboxylase
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Old 07-22-2012
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avidin from eggs bind biotin , results decrease of biotin . so long as biotin is cofactor of carboxylation reactions , then i guess carboxylase enzymes will get trouble too . but how to narrow down btn A and D , dont knw . bt will choose A .
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Old 07-23-2012
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Default correct answer :)

The answer is A) Acetyl-CoA carboxylase

I was actually confused btw A and E bc they are both ABC carboxylases so I couldn't decide on one or the other. I choose A but was wondering if there's any particular reason for that (like earlier manifestation of the deficiency of Acetyl CoA carboxylase than in Propionyl CoA carboxylase def or something else...?)

Quick reminder:

ABC carboxylases:

1) Pyruvate carboxylase (glukoneogenesis)
2) Propionyl CoA carboxylase (odd-chain FA metabolism)
3) Acetyl CoA carboxylase (FA synthesis)

The question comes from usmleconsult and here's their explanation (which by the way did not convince me ).

Eating 20 raw eggs a day causes biotin deficiency because avidin in the egg binds to the vitamin. In fatty acid biosynthesis, acetyl-CoA carboxylase catalyzes the rate-limiting step, which is the conversion of acetyl CoA to malonyl CoA. This is a typical ATP-dependent carboxylation, with enzyme-bound biotin serving as a carrier of the carboxyl group. Acetyl-CoA carboxylase is regulated by rapid-acting and slow-acting mechanisms. Short-term control involves allosteric activation by citrate and covalent modification. Long-term control involves changes in the concentration of the enzyme.

Propionyl-CoA carboxylase requires biotin, but it does not participate in fatty acid synthesis. It functions in a pathway from propionyl CoA to succinyl CoA. This pathway is involved in the oxidation of fatty acids that have an odd number of carbon atoms. The pathway also serves as a point of entry into the citric acid cycle for some of the carbon atoms of methionine, isoleucine, and valine.
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Old 07-23-2012
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may be i ddnt understand explanation given above , but for my level of understanding i dont see if they real make any reason behind of choosing A and not D as answer here . it seems they are trying just gve general details of story of these enzyme . Casandra can u make more clear in simple language ? thaks
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Old 07-23-2012
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Quote:
Originally Posted by koyi View Post
may be i ddnt understand explanation given above , but for my level of understanding i dont see if they real make any reason behind of choosing A and not D as answer here . it seems they are trying just gve general details of story of these enzyme . Casandra can u make more clear in simple language ? thaks
I wrote before that I choose A bc I thought that maybe deficiency of Acetyl CoA carboxylase would be clinically earlier manifested than deficiency of Propionyl CoA carboxylase. I don't have any other reasons behind my choice.
I posted this question to see if other members had some other ideas bc the official explanation did not convince me at all.
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