Enzyme kinetics Flashcards
How do kinetic expirements reveal enzyme properties?
-Experiments examine the amount of product (P) formed per unit of time (T)
-velocity (V) = Change in P/Change in T (represents change of a quantity)
-Velocity is the Rate of an enzyme-catalyzed reaction
-Initial velocity (Vo) is the velocity measure just after we add the substrate to the enzyme (at start of reaction)
-The reaction rate depends on the substrate concentration at the start of the reaction
-The reaction rate also depends on temperature and pH
Explain optimal pH in all enzymes
-The pH optimum reflects the participation of specific ionizable groups at the active site necessary for catalytic function
-The pH optimum is characteristic for each particular enzyme
How are initial velocities measured?
Describe the enzyme-substrate complex (ES)
Describe the transition state and product formation
What are the effects of increasing E and S in solution?
-Will increase the overall reaction rate
-hence, increasing E or increasing S will increase ES and Vo will increase accordingly
What is the Michaelis-Menten Equation?
What is the meaning of Km
-Measured in concentration units (mols/L)
-Equivalent to [S] when Vo = Vmax/2 (initial velocity is half the maximal attainable velocity)
-A smaller numerical value of Km reflects a higher affinity between enzyme and substrate
-Km values for typical enzymes range from 10^-3M to 10^-8M
-Can be thought of as a measure of the affinity of Enzyme for Substrate
What are the meaning of Vmax?
-Vmax is measure in units of concentration change (ie. mols/L of product formed) divided by time (mols/Lxsec)
-The maximum rate of reaction obtainable and occurs only when [S] is at a much greater concentration than the enzyme concentration [E]
-hence, Vmax is measured when [S]»[E]. This is termed ENZYME SATURATION
-The larger the numerical value of Vmax, the more quickly substrate is converted to product
Describe enzyme saturation
What is the effect of total enzyme concentration [Etotal] on Vmax?
-If [S] = constant, and [S]»[Etotal] then Vo is proportional to [Etotal]
-This is because: [Etotal] = [ES] under these conditions
What is kcat or turnover number?
Why is kcat useful?
What is the specificity constant?
