Enzyme Kinetics

v0

initial rate symbol

v0

the number of moles of product formed per second when the reaction is just beginning.

reaction rate

the amount of product formed in a unit time

reaction rate

tangent on the substrate→ product curve indicates the ____

v0

for enzyme kinetic analysis, ______ is used

stopped-flow apparatus

What is used to observe reactions during the first few milliseconds?

enzyme, subtrate

What determines the initial velocity (V₀) of an enzymatic reaction?

• the amount of _____ and ______

higher

The higher the amount of enzyme, the ______ the v0

saturated, higher

The higher the amount of substrate, within a limit:

• (before the enzyme being ____by the substrate)

• the ______ the v0

v0 = vmax

When all the active sites on enzymes are occupied by substrates:

• _______

substrate

Michaelis-Menten Equation:

• showing how the initial rate (V₀) of a reaction depends on the _______ concentration

v0 = vmax[S] / ( KM + [S] )

Michaelis-Menten Equation Formula

K1

rate constant for the formation of the ES complex

kcat

rate constant for converting the ES complex to product

kcat

k2 is also known as _______

substrate, ES complex, product

An enzyme first has to bind to a ______ to form the _____, which then either dissociates or proceeds to produce ______

binding, catalysis

enzyme-catalyzed reaction is a two-step process:

• the first step being _____

• the second step being ______.

k1, k_-1

The rate constants that govern binding step are _____ and _____

kcat

the rate constant hat governs the catalytic step is ______.

ES complex, kcat

the reaction rate is determined by the concentration of _______ and ______.

v0 = [ES] * kcat

enzyme-catalyzed reaction equation

half

KM is the substrate concentration where vmax is at ____ concentration

Kd

dissociation constant of ES complex

low

A _____ value of Kd means a higher affinity between two molecules.

k_-1 / k1

what is the Kd ratio?

tighter

A lower value of K_D indicates a ____ binding of E and S

kcat = vmax / [Et]

Formula used to derive kcat w/ ET

reversible, product, ES

What are 2 assumptions for deriving Michaelis-Menten equation?

• binding of E and S is ____

• _____ formation is rate limiting

  • Rate is dependent on concentration of ____

[S]

The benefit of measuring the initial rate of a reaction( V₀ )is that at the beginning of a reaction

• _____ is a CONSTANT

  • changes to this is negligible

steady state, constant

Steady-state assumption:

• during enzymatic reaction, ES quickly comes to ____ , so [ES] is _____ throughout the measured portion of the reaction.

k1, greater

According to the Steady-state assumption:

• ____ step is very fast

• [S] is ____ than [Et]

E, ES

What is the 4th assumption for deriving Michaelis-Menten equation?

• The enzyme exists in only two forms: ____ and ____

• Thus, [Et] (total enzyme) is the SUM of these two

kcat

turnover number; denotes how fast a bound substrate is processed by an enzyme

high

A low Km enzyme has _____ affinity to its substrates

low

A high Km enzyme has ____ affinity to its substrates

hexokinase, glucokinase

example of enzymes catalyzing the same reaction but with different K_m

• ______ and _____ w/ Glucose binding

most, low

Hexokinase is found in ____ cells and has a ____ K_m value

liver, high

Glucokinase is found in ____ and has a ____ K_m value

Hexokinase

Phosphorylates glucose for glycolysis

Glucokinase

Phosphorylates glucose for glycogen synthesis

hexokinase

the rate of ____ is NOT influenced by the fluctuation of glucose level in the blood.

glucokinase

________ has very high rate ONLY when blood glucose level INC , which occurs after a carbohydrate rich meal.

acetaldehyde

Metabolism of ethanol in our body produces an intermediate called ________

mitochondrial

This aldehyde dehydrogenase has very low Km

• thus, it has very high affinity to acetaldehyde, and it can remove acetaldehyde even if its level is very low;

cytoplasmic

This aldehyde dehydrogenase has very high Km

• its affinity to acetaldehyde is very low, and thus it can not effectively remove acetaldehyde when its level is not very high.

cytoplasmic

Asian populations have to use ______ aldehyde dehydrogenase to remove the toxic acetaldehyde, which causes acetaldehyde to accumulate to a toxic level

K cat / K m

catalytic efficiency can be determined through the ratio : _________

K cat / K m

a higher ratio of ______ means a more efficient enzyme

K1

the UPPER LIMIT of K cat / K m is _____

highest

a catalytic perfect enzyme has the _____ ratio of K cat / K m