Question

Give an example of an enzyme

Give a type of reaction

Name a pathway for each coenzyme/cofactor

For each:

Fe2+: found in Mb/Hb

Mg2+: stabilizes negative charges on ADP/ATP

Biotin: 1-C (carboxy) carrier

NAD+/NADH & FAD(H2): electron carriers (how many electrons?)

TPP: 2-C (acetaldehyde) carrier

Lipoate: acyl/acetyl group and electron carrier

Coenzyme A: acyl/acetyl carrier with thiol group

Answer 1

Answer:

i) Fe²⁺

• Name of enzyme having Fe²⁺ as cofactor is Cytochrome oxidase.
• It is the last enzyme in the respiratory electron transport chain, located in inner mitochondrial membrane.
• Cytochrome oxidase catalyzed the following redox reaction:

4 Fe²⁺-cytochrome c + 8 H⁺_in + O₂ ? 4 Fe³⁺-cytochrome c + 2 H₂O + 4 H⁺_out

ii) Mg²⁺

• Name of enzyme having Mg²⁺ as cofactor is phosphofructokinase-1
• In third step of glycolysis it catalyzes the transfer of a phosphoryl group from ATP to fructose 6-phosphate to yield fructose 1,6-bisphosphate.
• phosphofructokinase-1 catalyzed the reaction of transfer of phosphate from ATP to fructose 6-phosphate.

iii) Biotin

• Name of enzyme having biotin as coenzyme is pyruvate carboxylase.
• The reaction involves biotin as a carrier of activated HCO₃^–
• It catalyzed the reaction of conversion of the pyruvate to oxaloacetate. It is the first regulatory enzyme in the gluconeogenic pathway.

iv) NAD+/NADH & FAD(H2):

• Name of enzyme having NAD+/NADH & FAD(H2) as coenzyme is ?-ketoglutarate dehydrogenase complex.

• The reaction involves NAD+ serves as electron acceptor
• It catalyzed the reaction of oxidation of alpha ketoglutarate of citric acid cycle.

-Ketoglutarate + CoA +NAD <========è succinyl-CoA +CO2 +NADH+ H⁺

v) TPP (thiamine pyrophosphate)

• Name of enzyme having TPP (thiamine pyrophosphate) as coenzyme is transketolase.

• The reaction involves TPP is the transfer of a two carbon group, carried temporarily on enzyme-bound TPP, from a ketose donor to an aldose acceptor.
• It catalyzed the reaction of transfer of keto group in pentose phosphate pathway.

vi) Lipoate

• Name of enzyme having Lipoate as coenzyme is pyruvate dehydrogenase complex (dihydrolipoyl dehydrogenase).
• The reaction involves lipoate has two thiol groups that can undergo reversible oxidation to a disulfide bond. Because of its capacity to undergo oxidation-reduction reactions, lipoate can serve both as an electron hydrogen carrier and as an acyl carrier..
• It catalyzed the reaction of oxidative decarboxylation, in which the carboxyl group is removed from pyruvate as a molecule of CO2 and the two remaining carbons become the acetyl group of acetyl-CoA.

vii) Coenzyme A

• Name of enzyme having Coenzyme A as coenzyme is pyruvate dehydrogenase complex
• The reaction involves Coenzyme A has a reactive thiol (-SH) group that is critical to the role of CoA as an acyl carrier.
• It catalyzed the reaction of oxidative decarboxylation of pyruvate, to Acetyl-CoA and CO2 the acyl group attached to coenzyme A

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