Enzyme Kinetics

What does the Michaelis-Menten equation used for?

to describe enzyme kinetics

What does V0 mean in Michaelis Menten equation?

reaction velocity

What does V max mean in Michaelis Menten equation

Maximum possible reaction velocity

What does [S] mean in Michaelis Menten equation

Substrate concentration

What is the Km Michaelis Menten equation

Michaelis-Menten constant

What affect rate of enzyme-catalyzed reaction

• concentration of the substrate availablity

• Concentration of enzyme

• Enzyme identity

What is Isozyme:

Different enzymes that catalyze same reaction

Is steady state the same as equilibrium

NO

Irreversibility assumption of the Michaelis Menten equation: What is it?

Reaction proceeds in only one directions (ex: forward)

Michaelis Menten equation:

V0= Vmax [ S] // Km + [S]

What is the steady state assumption in the Michaelis Menten equation:

During experiment (ES) does not vary, so reaction velocity does not vary

• Vo = extrapolated initial velocity

What does the Free ligand approximation in the Michaelis Menten equation mean:

[Sfree]=[Stotal]

• [E] «[S] = total enzyme concentration is much smaller than substrate concentration

[Etotal] must be equal to…

[E] + [ES]

Michaelis Menten equation derrived:

[ES] = [Etot][S] / Km + [S]

V0 equation how to find it:

V0 = Kcat * [Etot][S] / Km + [S]

What does it mean when [ES] = [E tot]

This means that the enzyme is saturated & that the enzyme is operating at maximum rate

---

—> vmax = kcat [Etot]

What is the equilibrium dissociation constant?

kd = [P][L]/[PL]

What is the membrane transporters equation:

J0 = Jmax [C] = Kt + [C]

J = rate of transport (flux)

[C] = carried solute concentration

Kt = transport constant

The Michaelis constant, K_M, is defined as the product of the concentration of _____ ________ times the concentration of ______ _________, divided by the concentration of the ______-________ ___________.

The Michaelis constant, K_M, is defined as the product of the concentration of free enzyme times the concentration of free substrate divided by the concentration of the enzyme-substrate complex.

KM=[E][S]/[ES]

Fill in the table below describing the assumptions of the Michaelis-Menten equation:

The assumptions of the Michaelis-Menten equation:

In an enzyme-catalyzed reaction, the [substrate-binding/catalytic] step is typically assumed to be the slow, rate-determining step.

In an enzyme-catalyzed reaction, the catalytic step is typically assumed to be the slow, rate-determining step.

What is the mathematical relationship between k_cat, V_max, and [E_tot]?

Vmax=kcat[Etot]

An an axis which of the variables in the Michaelis-Menten equation are independent and dependent?

V0 is dependent (y axis)

[S] is independent (x axis)

What is the michaelis constant:

Km = [E][S]/[ES]

• affinity between enzyme and substrate

What does kd (equilibrium dissociation constant show us?

Shows us affinity between protein and ligrand

kd = [P][L]//[PL]

In Equilibrium dissociation constant, what does it mean when [L] (ligand concentration) is = to Kd?

It means that the protein is 50% saturated; 50% of the proteins are bound to ligand

What does it mean in the michaelis constant if the [S] (substrate concentration) is = to Km

It means that the rate is operating at 50% of vMax

What is intensive property?

properties that belong to the sample or substance itself regardless of amount

• density

• tempt

  • specific heat cap

What is extensive property

Properties that depend on the amount of sample or substance available

• mass and volume

• heat

• heat capacity

• Vmax

What is turnover number

It is the same as kCat (catalytic rate constant) = vmax / [E total]

What does Vmax tell you?

It tells you the maximal enzyme reaction rate

• depends on enzyme concentration [Etot]

What does turnover number tell you?

It tells you how many susbtrate molecules one enzyme “turns over” per unit time when saturated

If the Km value is small,

higher affinity

If the Kcat value is large

the faster the rate

Catalytic eficient equation

Kcat/Km

When [S] is low, V0 is…

Proportional to catalytic efficiency

What does it mean when the catalytic efficiency value is high

The faster the rate at low substrate concentrations (only when [S] is lower than km)

Catalytic perfection is

Catalytic efficiency > 10^8

What is the rate limiting step in catalytic perfection

Diffusion

How would an increase in catalytic efficiency be depicted on a Lineweaver-Burk plot?

An increase in catalytic efficiency (kcatKM) is depicted as a decrease in the slope (KMVmax=KMkcat × [Etot] ) of a Lineweaver-Burk plot.

Positive cooperativity allows for more rapid changes in reaction velocity—relative to noncooperative enzymes—when the substrate concentration is near the enzyme's K_M. (True or False)

True. Positive cooperativity allows for more rapid changes in reaction velocity—relative to noncooperative enzymes—when the substrate concentration is near the enzyme's K_M.

From a Michaelis-Menten plot, V_max equals the value of the horizontal asymptote, and K_M equals half that value (½V_max). (True or False)

False. From a Michaelis-Menten plot, V_max equals the value of the horizontal asymptote, and K_M equals the substrate concentration that results in half that value ([S] at ½V_max).

A Lineweaver-Burk plot whose y-intercept has shifted upward indicates that the V_max has [increased/decreased]. (Choose one option)

A Lineweaver-Burk plot whose y-intercept has shifted upward indicates that the V_max has decreased.

Fill in the blanks with a description of the value of the Hill coefficient n and the type of cooperativity described by the corresponding curve.

Enzyme cooperativity as seen on Michaelis-Menten plots:

A decrease in the K_M value is reflected in the Lineweaver-Burk plot as a shift of the x-intercept to the right. (True or False)

False. A decrease in the K_M value is reflected in the Lineweaver-Burk plot as a shift of the x-intercept to the left, away from the origin.

An increase in K_M is reflected as a(n) [upward/downward/rightward/leftward] shift of a Michaelis-Menten plot. (Choose one option)

An increase in K_M is reflected as a rightward shift of a Michaelis-Menten plot.

Give the equation that describes the Lineweaver-Burk plot.

The Lineweaver-Burk plot is a double reciprocal plot of its Michaelis-Menten counterpart and is described by the following equation, given in slope-intercept form:

1/V0=KM/Vmax⋅1/[S]+1/Vmax

The initial slope of a Michaelis-Menten plot is roughly proportional to the __________ ______________ of the enzyme.

The initial slope of a Michaelis-Menten plot is roughly proportional to the catalytic efficiency (k_cat/K_M) of the enzyme.

The x-intercept of a Lineweaver-Burk plot is equal to __________.

The x-intercept of a Lineweaver-Burk plot is equal to −1/K_M.