catalyzed by TPI, as illustrated at the beginning of Question #3. Explain why this step is suitable for measuring the flux of glycolysis through the release of H attached to the 3-C position of glucose?

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Chapter21: Carbohydrate- Controlled Diets For Diabetes Mellitus
Section: Chapter Questions
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(d)
of glucose oxidation in diabetic human patients treated
with Metformin (●) and in (nondiabetic) control human
patients (0). At –150 min both groups of subjects were
started on an intravenous feed of 3-(®H)-glucose, and at
t = 0 min they were started on an oral glucose tolerance
test whereby a measured amount of glucose in water (a
syrupy mixture) was swallowed followed by measure-
ment of blood glucose levels at 30 min intervals. The
flux of glucose oxidation was measured by the appear-
ance of 3H2O in the blood stream. While the information
The diagram to the right compares the rate
8000
ORAL
GLUCOSE
6000-
4000-
2000-
-120 -60
60
120
180 240 300
Minutes
cannot be directly extracted from the reaction mecha-
nism diagrams in the textbook, the glycolytic step in which the tritium is first released into water is that
catalyzed by TPI, as illustrated at the beginning of Question #3. Explain why this step is suitable for
measuring the flux of glycolysis through the release of °H attached to the 3-C position of glucose?
3H20 Specific Activity (dpm/ml)
Transcribed Image Text:(d) of glucose oxidation in diabetic human patients treated with Metformin (●) and in (nondiabetic) control human patients (0). At –150 min both groups of subjects were started on an intravenous feed of 3-(®H)-glucose, and at t = 0 min they were started on an oral glucose tolerance test whereby a measured amount of glucose in water (a syrupy mixture) was swallowed followed by measure- ment of blood glucose levels at 30 min intervals. The flux of glucose oxidation was measured by the appear- ance of 3H2O in the blood stream. While the information The diagram to the right compares the rate 8000 ORAL GLUCOSE 6000- 4000- 2000- -120 -60 60 120 180 240 300 Minutes cannot be directly extracted from the reaction mecha- nism diagrams in the textbook, the glycolytic step in which the tritium is first released into water is that catalyzed by TPI, as illustrated at the beginning of Question #3. Explain why this step is suitable for measuring the flux of glycolysis through the release of °H attached to the 3-C position of glucose? 3H20 Specific Activity (dpm/ml)
3. Triose-phosphate isomerase (TPI) catalyzes the movement of a single proton to interconvert dihy-
droxyacetone phosphate and glyceraldehyde 3-phosphate in glycolysis and gluconeogenesis. The
enzyme, a dimer of identical subunits that are 248 amino acids in humans, has no cofactors, required
metal ions, or cooperativity between subunits. The enzyme is found in all tissues. The value of
Kcat/ KM - 9.2 x 106 sec-'M-1 is close to the rate constant expected for a diffusion-limited reaction. The
mechanism of the proton transfer is illustrated in the diagram below.
Glu-165
Glu-165
Glu-165
O.
HR
ks
HR
k2
HR
OH
20,PO
20,PO
OH
HO
20,PO
His-95
His-95
His-95
Transcribed Image Text:3. Triose-phosphate isomerase (TPI) catalyzes the movement of a single proton to interconvert dihy- droxyacetone phosphate and glyceraldehyde 3-phosphate in glycolysis and gluconeogenesis. The enzyme, a dimer of identical subunits that are 248 amino acids in humans, has no cofactors, required metal ions, or cooperativity between subunits. The enzyme is found in all tissues. The value of Kcat/ KM - 9.2 x 106 sec-'M-1 is close to the rate constant expected for a diffusion-limited reaction. The mechanism of the proton transfer is illustrated in the diagram below. Glu-165 Glu-165 Glu-165 O. HR ks HR k2 HR OH 20,PO 20,PO OH HO 20,PO His-95 His-95 His-95
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