Ribulose-5-phosphate Epimerase Function
Ribulose-5-phosphate epimerase is an enzyme that catalyzes the reversible interconversion of D-ribulose-5-phosphate and D-xylulose-5-phosphate.
- Enzyme Activity: This specific epimerization reaction is a key step in metabolic pathways involving five-carbon sugars (pentoses).
- Pathway Involvement: The enzyme is crucial for the Pentose phosphate pathway (also known as the phosphogluconate pathway or hexose monophosphate shunt). This pathway generates NADPH and precursor pentose sugars for nucleotide biosynthesis.
- Intermediate Conversion: Specifically, Ribulose-5-phosphate epimerase converts ribulose-5-phosphate into xylulose-5-phosphate, which is then used in the non-oxidative phase of the pentose phosphate pathway for carbon rearrangement reactions.
Analysis of Options
- Glycolysis: This pathway breaks down glucose into pyruvate. Ribulose-5-phosphate epimerase is not directly involved.
- TCA cycle (Krebs cycle): This cycle oxidizes acetyl-CoA. It does not involve ribulose-5-phosphate epimerase.
- Glycosylation: This is the process of attaching carbohydrates to other molecules like proteins or lipids. While related to carbohydrates, this enzyme's specific function isn't glycosylation itself.
- Pentose phosphate pathway: This pathway directly utilizes and produces intermediates like ribulose-5-phosphate and xylulose-5-phosphate, making the epimerase essential for its operation.
Therefore, Ribulose-5-phosphate epimerase is involved in the Pentose phosphate pathway.
Important Questions from Metabolism Glycolysis Nucleotide
- The oxidative phase of the hexose monophosphate pathway generates ________ moles of NADPH per mole of glucose 6-phosphate (answer in integer).
- Which one of the following enzymes is NOT inhibited by glucose-6-phosphate?
- Assume that in the oxidative branch of the pentose phosphate pathway, each glucose-6-phosphate molecule generates the following products: 2 molecules of NADPH, 1 molecule of $\text{CO}_2$ and 1 molecule of ribulose-5-phosphate.
If 30 molecules of glucose-6-phosphate enter this pathway, and you randomly draw one molecule from the products of the pathway, the probability that this molecule is NADPH is __________ (round off to one decimal place). - Match the hormones in Group I with their metabolic precursor in Group II
Group I Group II P. 17-$\beta$ estradiol 1. Arachidonic acid Q. Thromboxane A2 2. Tyrosine R. Epinephrine 3. $\beta$-carotene S. Retinoic acid 4. Cholesterol Which of the following statements are TRUE for respiration?
P. The conversion of one molecule of pyruvate to three molecules of $CO_2$ generates four molecules of NADH
Q. Fructose 6-phospate is the principal substrate for glycolysis
R. The oxidation of glucose 6-phosphate to 6-phosphogluconate is the first step in the oxidative pentose phosphate pathway
S. The mitochondrial 'alternative oxidase' provides an alternative pathway for transfer of electrons from ubiquinone to oxygen utilizing proton pumping complex of the respiratory chain
