biochem

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Questions and Answers

Which electron acceptor is used for detection of succinate dehydrogenase or lactate dehydrogenase activity?

Indigo blue

Methylene blue (correct)

Acetone blue

Cobalt blue

What is one of the artificial electron acceptors used for detection of succinate dehydrogenase or lactate dehydrogenase activity?

Phenolphthalein

Bromothymol blue

Dichlorophenolindophenol (DCPI) (correct)

Thymolphthalein

Which enzyme activities can be detected using methylene blue and dichlorophenolindophenol (DCPI) as artificial electron acceptors?

Phosphatase and kinase

Catalase and peroxidase

Amylase and lipase

Succinate dehydrogenase and lactate dehydrogenase (correct)

In which state is dichlorophenolindophenol (DCPI) colorless?

Reduced Signup and view all the answers

What happens when electrons are transferred to dehydrogenase enzymes from succinate or lactate?

The reduction occurs Signup and view all the answers

Which chemical species has the highest redox potential?

DCPI Signup and view all the answers

What is the redox potential of NAD/NADH?

-0.06 V Signup and view all the answers

Which chemical species has the lowest redox potential?

FAD/FADH2 Signup and view all the answers

What can protons from FADH2 or NADH be transferred to?

Methylene blue or DCPI Signup and view all the answers

What is the effect of methylene blue or DCPI reduction in the reaction catalyzed by succinate or lactate dehydrogenase?

Gradual discoloration Signup and view all the answers

What are two competitive inhibitors of succinate dehydrogenase?

Malonate and pyrophosphate Signup and view all the answers

Which inhibitor has a similar structure to succinate?

Malonate Signup and view all the answers

What is the role of competitive inhibitors in enzyme reactions?

Compete with the substrate for the enzyme's active site Signup and view all the answers

What is the purpose of the SECOND experiment mentioned in the text?

Localization of enzymes in subcellular fractions of the liver Signup and view all the answers

Which enzymes are specifically targeted for localization in the SECOND experiment?

Succinate dehydrogenase, lactate dehydrogenase, and cytochrome oxidase Signup and view all the answers

What is the role of p-phenylenediamine in the context mentioned?

Acting as an artificial electron donor Signup and view all the answers

How does the redox potential of p-phenylenediamine compare to cytochrome c?

Slightly lower than cytochrome c Signup and view all the answers

What is required for the oxidation of p-phenylenediamine in the presence of oxygen?

Active cytochrome oxidase + sufficient cytochrome c Signup and view all the answers

What indicates the progress of the reaction involving p-phenylenediamine and oxygen?

Color appearance in tubes Signup and view all the answers

What is the dependency for the oxidation of p-phenylenediamine?

Cytochrome oxidase Signup and view all the answers

Study Notes

Enzyme Assays

Methylene blue and dichlorophenolindophenol (DCPI) are artificial electron acceptors used to detect succinate dehydrogenase or lactate dehydrogenase activity.

Redox Reactions

Electrons transferred from succinate or lactate to dehydrogenase enzymes reduce DCPI or methylene blue, resulting in a color change.
DCPI is colorless in its oxidized state.
The redox potential of NAD/NADH is -320 mV.

Redox Potentials

The chemical species with the highest redox potential is oxygen (O2).
The chemical species with the lowest redox potential is NADH.

Proton Transfer

Protons from FADH2 or NADH can be transferred to oxygen or other electron acceptors.

Enzyme Inhibition

Oxamic acid and malonate are competitive inhibitors of succinate dehydrogenase.
Malonate has a similar structure to succinate.

Enzyme Localization

The second experiment involves localizing succinate dehydrogenase and lactate dehydrogenase in tissue samples.

p-Phenylenediamine

p-Phenylenediamine is an electron acceptor with a redox potential higher than that of cytochrome c.
Oxygen is required for the oxidation of p-phenylenediamine.
The formation of a purple color indicates the progress of the reaction involving p-phenylenediamine and oxygen.
The oxidation of p-phenylenediamine depends on the presence of oxygen.

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Description

Test your knowledge of electron acceptors used in enzyme activity detection with this quiz. Explore the roles of methylene blue and dichlorophenolindophenol (DCPI) in detecting succinate dehydrogenase or lactate dehydrogenase activity.