enzymes o -co -c hi, everybody! objectives enzymes as biological catalysts the properties of enzymes...

EnzymesO -

C

Hi, Everybody!Hi, Everybody!

Objectives Objectives

Enzymes as Biological Catalysts

The Properties of Enzymes

Enzyme classification

Substrate Binding and

Enzyme Action

Enzyme Inhibition

Regulation of enzyme activity.

Applications of Enzyme Action

Intended learning outcomes(ILO)

Intended learning outcomes(ILO)

State the different properties of enzymes.

2-PROPERTIES OF ENZYMES

2-PROPERTIES OF ENZYMES

Enzymes properties1-All enzymes are proteins

2-Enzymes do not determine the direction of reaction

3- Enzymes are highly specific

4-Some enzymes require cofactors

• Ribozymes= Small group of catalytic RNA molecule which share in the posttranscriptional modification of nascent RNA.

Pre-mRNA Mature mRNA

Ribozyme

Cleave phosphodiester bond of RNA

1-All enzymes are proteins except ribozymes

2-Enzymes do not determine the direction of reaction

They only accelerate reaching the equilibrium

state.

The direction of the reaction is determined by the free energy change of

the reaction=ΔG

From reactants to products

OrFrom products to

reactants

3 -Enzymes are highly specific

TO their Substrate

To the reaction

3-Enzymes are the most specific catalyst

Enzyme specificity

• The enzyme is specific for one substrate e.g.

• glucokinase act only on glucose but not other hexoses.

• Urease acts on urea.Absolute

specificity

• Enzymes Catalyze the same type of reaction on a number of structurally related substrates having the same type of bond.

• Hexokinase act on glucose, fructose, mannose

• Peptidase acts on peptide bonds in different proteins.

Relative specificity

Enzyme specificity

• The enzyme is directing not only to the type of bond but also to the site of bond and the groups around it .

• Chemotrypsin acts on peptide bonds formed by certain amino acids

Group specificity

• The enzyme are specific to the D- or to the L- isomer but not both.

• e.g. L-amino acid oxidase for L-amino acids not for D-AA.

Stereospecificity

Enzyme specificity

Specificity of Ser-Protease Family

COO-

CAsp

COO-

CAsp

Active Site

Trypsin Chymotrypsin Elastasecut at Lys, Arg cut at Trp, Phe, Tyr cut at Ala, Gly

Non-polarpocket

Dee

p an

d ne

gativ

ely

char

ged

pock

et Shallow andnon-polar

pocket

O O–C–N–C–C–N –

C C C C NH3+

O O–C–N–C–C–N –

C

O O–C–N–C–C–N –

CH3

Jua

ng

RH

(2

00

4)

BC

ba

sics

Some enzymes require a cofactor

Let’s meetthe team…

Cofactors

Metal ions)Mg, Fe, Cu(

Coenzymes non protein, low molecular weight

Usually derived from vitamins, heat stable

Bind loosely with enzymeFew bind firmly(prothestic group)

Regenerated after reaction

NON protein part

coenzymes Metal ion

NON protein part

coenzymes Metal ion

Metalloenzyme(tightly bound)

Glutathione peroxidase contain

Se

Metal activated enzymes(loosely

bound)Coagulation enzymes

require Ca in blood

NON protein part

coenzymes

Tightly bound(Prosthetic group)

Loosely bound, e.g. NAD

Cofactors(metal)

NON protein part

coenzymes

Tightly bound(Prosthetic group)

Covalently bound

e.g. biotin, heme

Non covalently bound

e.g. FMN

Loosely bound, e.g.

NAD

Cofactors(metal)

NON protein part

coenzymes

Tightly bound(Prosthetic group)

Covalently bound

e.g. biotin, heme

Non covalently

bounde.g. FMN

Loosely bound,

e.g. NAD

Cofactors(metal)

Metalloenzyme(tightly boundGlutathione peroxidase contain Se

Metal activated enzymes(loosely

bound)Coagulation

enzymes require Ca in blood

Apoenzymes, coenzymes holoenzymes

Let’s meetthe team…

Apoenzyme (protein part )

Coenzymes(non protein part)

Holoenzyme

)active catalytic unit(

Some enzymes require cofactors

Are specific non-protein organic or metallo-organic heat stable low molecular weight compounds required for the activity of the enzyme:

Co-enzymes

Co-enzymes acts asTransient carrier of

specific functional groups or atoms

•NAD carries the hydride ion during oxidation reduction reaction.

Co-substrate(second substrate)

•Coenzymes has affinity for the enzyme similar to that of the substrate.

•The chemical changes in the coenzymes counterbalance those occurring in the substrate.

•If the substrate is oxidized, the coenzyme is reduced

• The changes occurring in the coenzyme may more important than that occurring in the substrate.

• The reaction catalyzed by lactate dehydrogenase is mainly for oxidation of NADHH rather than reduction of pyruvate to lactate

Co-enzymes

Vitamin Co-enzyme Function

Thiamine ( B1) TPP Oxidative decarboxylation

Riboflavin (B2) FAD,FMN

Dehydrogenation

Lipoic acid Lipoic acid Oxidative decarboxylation

Niacine NAD,NADP

Dehydrogenation

Pyrodoxine PLP Amino acid metabolism

Biotin Biotin carboxylation reaction

Pantothenic Acid

CoA SH 1.Carobydrates,fat and lipids metabolism

Folic Acid THF One carbon unit metabolism

Co-enzymes derived from vitamins