The catalytic efficiency of many enzymes depends on pH. Chymotrypsin shows a maximum value of kaKM at pH 8. Detailed analysis shows that kat increases rapidly between pH 6 and 7 and remains constant at higher pH. KM increases rapidly between pH 8 and 10. Suggest explanations for these observations.
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- Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved residues in slightly different positions can change the catalytic rate of reaction.Understanding Enzyme Mechanisms Related to Pyruvate Carboxylase Based on the mechanism for pyruvate carboxylase (Figure 22.3), write reasonable mechanisms for the reactions that follow:Understanding a Ubiquitous Series of Metabolic Reactions Study Figure 23.9. Where else in metabolism have you seen the chemical strategy and logic of the -oxidation pathway? Why is it that these two pathways are carrying out the same chemistry?
- Why Do Anabolic and Catabolic Pathways Differ? Why is the pathway for the biosynthesis of a biomolecule at least partially different from the pathway for its catabolism? Why is the pathway for the biosynthesis of a biomolecule inherently more complex than the pathway for its degradation?The Effect of lodoacetic Acid on the Glyceraldehyde-3-P Dehydrogenase Reaction (Integrates with Chapters 4 and 14.) How might iodoacetic acid affect the glyceraldehydes-3-phosphate dehydrogenase reaction in glycolysis? Justify your answer.Studies at diff erent pH’s show that an enzyme has two catalytically important residues whose pKs are ∼4 and ∼10. Chemical modifi cation experiments indicate that a Glu and a Lys residue are essential for activity. Match the residues to their pKs and explain whether they are likely to act as acid or base catalysts.
- When enzyme solutions are heated, there is a progessive loss of catalytic activty over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 45 degrees Celsius lost 50% of its activity in 12 minutes, but when incubated at 45 degrees Celsius in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 minutes. Suggest why thermal denaturation of hexokinase was retarded in the presence of one substrates.The above reaction coordinate diagram in the presence of enzyme is inconsistent with the "lock and key" model of enzyme-substrate l binding. Draw and properly label the reaction. coordinate diagram for the enzymatic reaction according to the "lock and key" model. Explain why this model is inconsistent with catalytic properties of enzymes.When enzyme solutions are heated, there is a progressive loss of catalytic activity over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 45 °C lost 50% of its activity in 12 min, but when incubated at 45 °C in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 min. Suggest why thermal denaturation of hexokinase was retarded in the presence of one of its substrates.
- Many isolated enzymes, if incubated at 37°C, will be denatured. However, if the enzymes are incubated at 37°C in the presence of substrate, the enzymes are catalytically active. Explain this apparent paradox.when saturated with substrate, an enzyme has a maximum initial rate of 110mumoles of substrate converted to product per second. At a substrate concentration of 100mu M, the same enzyme converts substrate to product at a rate of 0.010mmoles/ sec. Assuming that Michaelis - Menten kinetics are followed, calculate the reaction rate when substrate concentration is 2x10^-3M.A direct measurement of the standard free-energy change associated with the hydrolysis of ATP is technically demanding because the minute amount of ATP remaining at equilibrium is difficult to measure accurately. The value of ΔG′° can be calculated indirectly, however, from theequilibrium constants of two other enzymatic reactions having less favorable equilibrium constants:Using this information for equilibrium constants determined at 25 °C, calculate the standard free energy of hydrolysis of ATP.