Enzymes

Biochemistry for nurses

ENZYMES


Enzymes are biocatalysts that speed up biochemical reactions (mostly

involved in the digestion and metabolism reactions)

Enzymes are not destroyed in their reactions; they are used over and

over again

Chemicals reacting with enzymes are called Substrates Substrate (S) binds to enzyme (E) during its reaction to form a product (P):

E + S ES P + ESimplest case!

Enzymes definition


Enzymes definition


Enzymes catalyze biological reactions

Enzymes have very strong catalytic power; rate of reactions can be

million or billion times faster than those in absence of enzymes

Ex: Oxidation (burning) of Glucose, by Glucose Oxidase (enzyme),

catalyzes glucose to react with oxygen (O2) with a very high-energy

release. However, exposing a container of glucose to the air (O2) for

years will cause no detectable reaction.


Glucose oxidase is widely used for the determination of free glucose in sera or blood

plasma for diagnostics, using spectrometric assays.

Example:


Enzymes catalyze biological reactions

Enzyme catalysts reduce the activation

energy required, thereby increasing the

rate of reaction.


The reaction goes very fast in the presence of Enzymes!

More examples:Enzyme Substrate Product Rate without

enzyme (umoles/liter per

min)

Rate with enzyme

(umoles/liter per min)

Acceleration due to Enzyme

Hexokinase Glucose Glucose 6-P < 0.0000001 1300 X 13 billion

Alcohol dehydrogenase

Ethanol Acetaldehyde < 0.000006 2700 X 450 million

Creatine-Kinase

Creatine Creatine phosphate

< 0.003 40 X 13,000


Substrates Bind to the Active Sites of Enzymes


Substrates Bind to the Active Sites of Enzymes

Example: DNA polymerase


Example:


Classification


The Maximun Rate of an Enzymatic Reaction is Proportional to the Substrate Concentration!

AB

C

X

Saturation point

-----------------------Rmax (Maximun rate)

[Enzyme] = Constant


Effect of Enzyme Concentration on the Reaction Rate

In case of a substrate concentration unlimited, an increase of the enzyme concentration causes an increase of the reaction rate!

More enzymes can react with more substrate molecules

[S]= ∞

[E] Rate



[E1] > [E2]

[E1] < [E2] ???



[E1] > [E2]

[E1] < [E2]


Enzymes are Very Sensitive to Change in pH

Enzyme have a pH optimum, i.e. they have optimal activity at certain pH

Most enzyme exhibit optimal activity at pH value between 5 and 9 If the pH is too low (high H+ concentration) or too high (low H+

concentration) the enzyme activity will fall pH sensitivity is due to an ionization of the enzyme which results in

denaturation of enzyme (change in protein structure will cause

precipitation = loss of solubility of enzyme protein in water)


Enzymes are Very Sensitive to Change in pH


Enzymes are Adapted to their pH Environment

Cells, blood and saliva have a pH close to 7

Stomach has a pH of 1-2 during digestion.

The graphe below shows the activities of 2 different enzymes, one

adapted to work in the stomach (Pepsin) and the other adapted to work

in the small intestine (Trypsin).


Enzymes are Very Sensitive to Change in Temperature

Enzyme activity increases with

temperature up to about 45°C

With increasing temperature the

kinetic movement of enzyme and

substrate molecule increases, and

the chances of interaction between

enzyme and substrate molecule is

also increased, thereby

increasing the rate of reaction.


Enzymes are Very Sensitive to Change in Temperature

Denaturation of enzyme by temperature is IRREVERSIBLE!!


CoENZYMES and CoFactors

CoEnzymes and CoFactors are molecules which

are required for the enzyme activity.

CoEnzymes and CoFactors are not proteins! Many enzymes cannot function without them!!


ApoEnzyme = Inactive Enzyme HoloEnzyme = Active Enzyme


Examples of Vitamin and their coEnzymatic Function


CoENZYMES and CoFactors function

ApoEnzymeHoloEnzyme

HoloEnzyme


Conjugated Enzyme Structure

Some apoEnzymes need both a coEnzyme and a CoFactor

to become active!

HoloEnzymes


In living cells, all these reactions need Enzymes to function!!

Metabolism: The sum of chemicals reaction in a living cell

Catabolism: The process in which molecules are broken down to release

energy. Some of the energy released is captured for the synthesis of ATP

Anabolism: The process by which large molecules are synthesized using

smaller molecules that uses energy provided by ATP molecules.

Education

Enzymes