# 5 and 6 CASE 20 NAD otcus tenax but is also involved in providing intermediate
ID: 270657 • Letter: #
Question
# 5 and 6
CASE 20 NAD otcus tenax but is also involved in providing intermediates for cellular biosynthetic reactions. The gene for the non-phosphorylating, NAD -dependent GAPDH was cloned and sequenced and its kinetic characteristics were studied. Summary information is presented in Table 20.1 Table 20.1: Kinetic of NAD GAPDH isolated from T. tenax NAD saturation Without AMP 365 3.3 KM, mM Wih AMP 7.0 KM, mM Molecular Mass Subunit (kD) Native (kD) 55,000 220,000 Questions . Name the three enzymes that catalyze irreversible, regulated reactions in glycolysis as studied in class. 2. What is the significance of the GAPDH reaction in E. coli to glycolysis? . How does the reaction catalyzed by GAPDH from T. tenax presented here differ from the reaction carried out in E. coli? 4. The activity of the GAPDH enzyme was assayed in the presence of a constant amount of glyceraldehyde-3-phosphate and an increasing amount of NAD. The activity of the control was compared to the activity in the presence of various metabolites. The results are shown in Figure 20.2 Additional data are given in Table 20.2 a. Use the data in Figure 20.2 to estimate a Ku value for the enzyme in the presence of these metabolites. Classify the metabolites listed in Table 20.2 as inhibitors or activators. Fill in your answers in the table provided. Explain how you decided whether these metabolites are inhibitors or activators, based on the graph. How would you classify NADH, ADP and ATP? (These data are not presented in the graph). Are they inhibitors or activators? Add this information to Table 20.2. Explain the physiological significance of your answers to questions 4a and 4b b.
Explanation / Answer
Answer: The three irreversible regulated steps and the enzymes involved all belong to "kinase" category. Kinases are those enzymes which add phosphate to substrate and cause "phosphorylation"
The enzymes are
1. Hexokinase/glucokinase
2. Phosphoglycerate kinase
3. Pyruvate kinase
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