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.
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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.
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- In 1966, Ferdinand showed that a random-order ternary-complex mechanism for a two-substrate enzyme-catalysed reaction can lead to sigmoidal kinetics being observation in the absence of cooperative binding. Discuss this scenario so that it is clear why a plot of Vo versus [AXo] at constant [Bo] will be sigmoidal.Phospholipases show an enhanced activity for a substrateabove the critical micelle concentration. (The critical micelleconcentration, or cmc, is that concentration of a lipid abovewhich micelles begin to form.)a. What type of noncovalent interactions are possiblebetween the lipid and the enzyme at this stage?b. What do these interactions suggest about the structure ofphospholipases?Diagram the hydrogen-bonding interactions of the catalytic triad His–Lys–Ser during catalysis in a hypothetical hydrolytic enzyme.
- 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.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.During a test of kinetics of an enzyme-catalyzed reaction, the following data were recorded: a. Determine the Michaelis-Menten constant for the reaction with no inhibitor present at 30 °C and at 49.6 °C. b. Determine the maximum velocity of the uninhibited reaction at 30 °C and an enzyme concentration of 1.6 g/L. c. Determine the Ki for the inhibitor at 30 °C and decide what type of inhibitor is being used.