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An individual with chronic hypoglycemia was suspected of having a defect in one of the enzymes unique to gluconeogenesis. To identify the defective enzyme, tissue samples from a normal liver were compared to samples from the patient's liver biopsy, using a biochemical assay that measures glucose production from glycerol or malate. It was found that incubation with glycerol produced normal amounts of glucose in both the control and biopsied liver samples; however, incubation with malate did not lead to glucose production in the liver biopsy, even though it did lead to glucose production in the control liver sample. Based on these observations which of the 4 unique gluconeogenesis enzymes is most likely defective in the individual?

An individual with chronic hypoglycemia was suspected of having a defect in one of the enzymes unique to gluconeogenesis. To identify the defective enzyme, tissue samples from a normal liver were compared to samples from the patient's liver biopsy, using a biochemical assay that measures glucose production from glycerol or malate. It was found that incubation with glycerol produced normal amounts of glucose in both the control and biopsied liver samples; however, incubation with malate did not lead to glucose production in the liver biopsy, even though it did lead to glucose production in the control liver sample. Based on these observations which of the 4 unique gluconeogenesis enzymes is most likely defective in the individual?

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
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An individual with chronic hypoglycemia was suspected of having a defect in one of the enzymes unique to gluconeogenesis. To identify the defective enzyme, tissue samples from a normal liver were compared to samples from the patient's liver biopsy, using a biochemical assay that measures glucose production from glycerol or malate.

It was found that incubation with glycerol produced normal amounts of glucose in both the control and biopsied liver samples; however, incubation with malate did not lead to glucose production in the liver biopsy, even though it did lead to glucose production in the control liver sample.


Based on these observations which of the 4 unique gluconeogenesis enzymes is most likely defective in the individual? Consider each enzyme and explain your choice, including why you ruled out enzymes that you did not choose. To answer this question review how glycerol enters gluconeogenesis (figure 9.48) and how citrate cycle metabolites are transported in and out of the mitochondria (figure 10.39). 

The breakthrough came in 1917 when the American food chemist James Currie discovered that large amounts of citric acid in the form of citrate could be isolated from the mold Aspergillus niger when it was grown in a medium containing sucrose, salts, and iron. Currie teamed up with the chemical company Pfizer to develop proprietary methods to isolate large amounts of citrate from liquid Aspergillus cultures. Using optimized fermentation conditions, which take advantage of genetically selected Aspergillus strains, modern biotechnology methods can efficiently convert sucrose into citrate over a 10-day period by maintaining a constant biomass (Figure 10.39). Under these conditions, the fungi are functioning as bioreactors by converting most of the sucrose to citrate, rather than diverting it into metabolic reactions to support cell division, which would ultimately decrease citrate yields. These closely guarded fermentation methods produce nearly 500,000 metric tons of citric acid annually. Relative concentration 1.0 0.5 0 2 4 6 8 Citrate Biomass Sucrose 10 Aspergillus fermentation (days) Figure 10.39 Most commercial citric acid is derived from a fermentation process using the mold Aspergillus, which efficiently converts sucrose to citrate, the conjuga base of citric acid. The schematic graph shows the relative conversion of sucrose to citrate by Aspergillus over a 10-day period of fermentation. Notice that citrate production continues to rise even after a steady-state lev of Aspergillus cell mass (biomass) has been reached.
Transcribed Image Text:The breakthrough came in 1917 when the American food chemist James Currie discovered that large amounts of citric acid in the form of citrate could be isolated from the mold Aspergillus niger when it was grown in a medium containing sucrose, salts, and iron. Currie teamed up with the chemical company Pfizer to develop proprietary methods to isolate large amounts of citrate from liquid Aspergillus cultures. Using optimized fermentation conditions, which take advantage of genetically selected Aspergillus strains, modern biotechnology methods can efficiently convert sucrose into citrate over a 10-day period by maintaining a constant biomass (Figure 10.39). Under these conditions, the fungi are functioning as bioreactors by converting most of the sucrose to citrate, rather than diverting it into metabolic reactions to support cell division, which would ultimately decrease citrate yields. These closely guarded fermentation methods produce nearly 500,000 metric tons of citric acid annually. Relative concentration 1.0 0.5 0 2 4 6 8 Citrate Biomass Sucrose 10 Aspergillus fermentation (days) Figure 10.39 Most commercial citric acid is derived from a fermentation process using the mold Aspergillus, which efficiently converts sucrose to citrate, the conjuga base of citric acid. The schematic graph shows the relative conversion of sucrose to citrate by Aspergillus over a 10-day period of fermentation. Notice that citrate production continues to rise even after a steady-state lev of Aspergillus cell mass (biomass) has been reached.
Ethanol :......: Anaerobic metabolism Glycolysis NAD + NADH+ ATP Glucose Fermentation Pyruvate Citrate cycle Mitochondria NAD ATP + NADH Lactate dehydrogenase 2 ATP + Lactate 28 ATP NAD Electron transport NADH H₂O O 2 ADP + P; Oxidative phosphorylation CO2, H2O Aerobic metabolism Figure 9.48 Pyruvate has three metabolic fates, dependi on the type of organism and the availability of oxygen. Under aerobic conditions, pyruvate is metabolized in the mitochondria to produce CO2 and H₂O. When oxygen is limited, however, pyruvate is converted to lactate or ethanol (fermentation). The net 32 ATP shown for oxidative phosphorylation is based on 2 ATP generated i the cytosol by substrate-level phosphorylation in glycolysis and 30 ATP generated in mitochondria (2 ATI generated by substrate-level phosphorylation in the citra cycle and 28 by ATP synthase during oxidative phosphorylation).
Transcribed Image Text:Ethanol :......: Anaerobic metabolism Glycolysis NAD + NADH+ ATP Glucose Fermentation Pyruvate Citrate cycle Mitochondria NAD ATP + NADH Lactate dehydrogenase 2 ATP + Lactate 28 ATP NAD Electron transport NADH H₂O O 2 ADP + P; Oxidative phosphorylation CO2, H2O Aerobic metabolism Figure 9.48 Pyruvate has three metabolic fates, dependi on the type of organism and the availability of oxygen. Under aerobic conditions, pyruvate is metabolized in the mitochondria to produce CO2 and H₂O. When oxygen is limited, however, pyruvate is converted to lactate or ethanol (fermentation). The net 32 ATP shown for oxidative phosphorylation is based on 2 ATP generated i the cytosol by substrate-level phosphorylation in glycolysis and 30 ATP generated in mitochondria (2 ATI generated by substrate-level phosphorylation in the citra cycle and 28 by ATP synthase during oxidative phosphorylation).
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