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What does peroxidase do to potatoes immersed in a pH of 2, and a pH of 9,  and also...

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najlaalth | Student, Undergraduate | (Level 1) Salutatorian

Posted March 17, 2012 at 8:33 AM via web

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What does peroxidase do to potatoes immersed in a pH of 2, and a pH of 9,  and also adding hydrogen peroxide to the mixtures?

Peroxidase activity.....How does pH effect peroxidase activity?

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bandmanjoe | Middle School Teacher | (Level 1) Senior Educator

Posted March 18, 2012 at 11:21 AM (Answer #1)

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Peroxidase is an enzyme that can act as a nucleophilic acceptor or electrophilic acceptor.  So when potatoes are immersed in a pH of 2, this would be the acidic side of the pH scale.  Acids are substances that, when mixed with water, dissociate into hydrogen ions (H+).  This would be the nucleophilic side of the peroxidase.  A pH of 9 would clearly place the peroxidase on the basic side of the pH scale.  Bases are substances that, upon mixing with water, dissociate into hydroxide ions (OH-).  This would be the electrophilic side of the peroxidase.  And as for adding hydrogen peroxide to the mixtures, that would facilitate the peroxidase even more, as the standard electron acceptor for peroxidase action just happens to be hydrogen peroxide.  So peroxidase is enzymatic activity that would promote the breakdown of the molecules in the potato by nucleophilic and electrophilic transfer.

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najlaalth | Student, Undergraduate | (Level 1) Salutatorian

Posted March 18, 2012 at 12:04 PM (Answer #2)

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I thought that a strong acid either denatures an enzyme....and a strong base slows down the reaction, and since Ph2 is a strong acid would'nt that denature the peroxidase and stops the reaction from occuring?

 

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txmedteach | High School Teacher | (Level 3) Associate Educator

Posted March 18, 2012 at 12:27 PM (Answer #3)

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It depends on the conditions in which the enzyme operates best. For example, pepsin, a protease in the stomach, only functions at a pH of 2 and is denatured at higher pH's. In fact, any enzyme has both an upper and lower bound for pH's at which it can operate, and outside this range, enzymes will denature whether it is too acidic or too basic.

It just happens to be that peroxidases have an optimal pH near our blood ph (7.35-7.45), and they can function between a pH of 5 and 9. If the environment is any more acidic than a pH of 5 or any more basic than a pH of 9, the enzyme will denature.

Keep in mind what denature means, too! Enzymes are held together by interactions between polar parts, nonpolar parts, and eternal water. At high pH's, postive charges cannot be maintained, so if a positive charge is needed to keep an enzyme together, then a basic environment will deprotonate that amino acid and cause a shape change and denaturation. A similar effect occurs with negative charges and too acidic of an environment. This is why any pH lower than 7.35 or higher than 7.45 is bad news in your blood!

I hope that makes sense!

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