Enzymes 2 Flashcards
Describe a first order reaction
velocity of a reaction is directly proportional to reactant concentration, the reaction
V= k[A]
Units are s^-1
Describe a bimolecular (ssecond order reaction)
look like: 2A →P or A + B → P
Rate equation looks like: V = k[A]^2 or V = k[A][B]
proportionality constant for second-order reactions has the units M^-1 S^-1.
E + S → ES → E + P (E = enzyme, S = substrate, P = product)
Reaction velocity depends on the conc. of ES (complex)
Vi = k3[ES]
k3 = catalytic constant or turnover number (how much product is being made per second by the enzyme)
When does steady state occur in Michaelis-Menten kinetics?
Steady-State occurs for M-M kinetics when d[ES]/dt = 0, i.e., the rate of formation of [ES] = its rate of disappearance.
Rate during this time is defined as the Initial Velocity (vi)
What is the mass balance equation for enzymes?
E tot = [E] + [ES]
Etot = total enzyme count
E = enzyme ES = Enzyme substrate complex
also assume rate of breakdown for ES = 0
What is the equation for total substrate?
S tot = [S] + [ES]
Vo (velocity) is equal to what?
Vo = k2[ES]
How can rate of product formation be found?
Vnet = dP/dt = k[ES]
What is the assumption made about [ES] at steady state?
We assume that the rate of formation of [ES] is equal to the rate of breakdown of [ES]. We get the equation:
[E] [S] / [ES] = k-1 (reverse reaction) + k2/k1
Define the Michaelis constant Km as an equation and describe what it is.
Km = (k-1(reverse reaction) + k2) / k1
Km is the substrate concentration at which the reaction rate is half of Vmax. It represents an enzymes affinity for a substrate. Low = high affinity, High = low affinity
How would you find the total amount of free enzyme in a reaction?
[E] = [E] tot - [ES]
subtracting the total enzyme complex count from the total enzyme count will give the concentration of free enzymes.
Knowing that Km = (k-1(reverse reaction) + k2) / k1, how would the [ES] steady state equation change
[E] [S] / [ES] = k-1 (reverse reaction) + k2/k1
becomes
[ES] = [E] [S] / Km
How would [E] be substituted in the steady state equation given [E] = [E] tot - [ES]?
[ES] = ( [E]tot - [ES] ) [S] ) / Km
