BIOKIMIA MEDICINE

BIOKIMIA MEDICINE

SUBEHAN,

SUBEHAN, M.Pharm

.Sc

M.Pharm

.Sc., PhD

., PhD

ENZYMES

ENZYMES

MEC

HANIS

M O

F ACT

ION, IN

HIB

ITIO

N &

DIS

FUNCT

ION

MEC

HANIS

M O

F ACT

ION, IN

HIB

ITIO

N &

DIS

FUNCT

ION

INTRODUCTION

INTRODUCTION

�Enzymes are biological catalysis

-substance of biological origin that accelerate

chemical reactions.

-the vast majority of enzyme are proteins.

-catalytically active ribonucleic acids “ribozymes”.

-in general, name suffix “-ase”

�The presence and m

aintenance of a complete and

balanced set of enzymes is essential for

-the breakdown of nutrients to supply energy, and

chemical building block;

-the assembly of those building blocks into proteins,

DNA, membranes, cells, and tissues;

-and the harnessing of energy to power cell motility and

muscle contraction.

��Deficiency in quantity and catalytic activity

Deficiency in quantity and catalytic activity

can result from:

can result from:

-genetic defects,

-nutritional deficits,

-or, toxins.

��Defective enzymes can result from:

Defective enzymes can result from:

-genetic m

utation

-infections by viral or bacterial pathogens.

��Medical scientists:

Medical scientists:

-imbalances in enzyme activity

pharm

acologic agent to inhibit.

-investigating gene therapy

remedy deficits in enzyme level and function.

Enzyme activity

Enzyme activity

International unit, U: µmolturnover min

-1

1 U = 16.7 nkat

-Catalyze the conversion of one/more

compounds (substrate) into one/more

different compounds

Turnover (m

ol product s-1) with enzyme

Enzyme activity (mol s-1= kat)

Turnover (m

ol product s-1)

without enzyme

-Enhance the rate of the corresponding

noncatalyzedreaction by > 106

-Neither consumed nor perm

anently

altered in the reaction.

-Selective catalyst.

substrate piruvat------------

L-lactate.

Enzyme Nomenclature

Enzyme Nomenclature

International Union of Biochemist (IUB)

International Union of Biochemist (IUB)

��In general:

In general:

--Type of reaction catalyzed followed by suffix

Type of reaction catalyzed followed by suffix ––ase

ase..

-dehydrogenase, protease, etc.

��IUB:

IUB:

--Each enzyme has a unique name and code number that reflect the

Each enzyme has a unique name and code number that reflect the type of

type of

reaction catalyzed and the substrate involved.

reaction catalyzed and the substrate involved.

--EC 1.2.3.4

EC 1.2.3.4

--EC, Enzyme catalog

EC, Enzyme catalog

--1, Class

1, Class

--2, subclasses

2, subclasses

--3,

3, subsubclasses

subsubclasses

--4, where the enzyme belongs in the

4, where the enzyme belongs in the subsubclases

subsubclases..

--EC 2.7.1.1

--class 2,

class 2, transferase

transferase

--subclass 7, transfer of a

subclass 7, transfer of a phosphoryl

phosphorylgroup.

group.

--subsubclass

subsubclass1, alcohol is the

1, alcohol is the phosphoryl

phosphorylacceptor.

acceptor.

--1, hexose

1, hexose-- 6, alcohol

6, alcohol phosphorylated

phosphorylatedis the of carbon

is the of carbon-- 6 of a

6 of a hexose

hexose..

Enzyme Classes (IUB)

Enzyme Classes (IUB)

Annotated enzyme list

�Only the enzymes mentioned in this atlas are listed here, from among the

more than 2000enzymes known.

�The enzyme names are based on the IUBMB’sofficial Enzyme

nomenclature1992.

�The additions shown in round brackets belong to the enzyme name,while

prostheticgroups and other cofactors are enclosed in square brackets.

�Common names of enzyme groupsare given in italics, and trivial names are

shown in quotation marks.

Enzyme Catalysis

Enzyme Catalysis

UNCATALYZED REACTION

ENZYME-CATALYZED REACTION

Active site

1. Free enzyme E

2. E•A-complex

3. E•A•B-complex

4. Transition state E╪ ╪╪╪

5. E•C•D-complex

6. E•D-complex

Principle of enzyme catalysis

Principle of enzyme catalysis

Approximation and orientation

of the substrates

XY

Z

Exclusion

of water

Stabilization of

the transition state

Group

of transfer

Principles of enzyme catalysis

Principles of enzyme catalysis

Mechanism for catalysis by an aspartic protease

Mechanism for catalysis by an aspartic protease

1.AspartateX actsas a base to activate a water molecule by abstracting a

proton.

2.The activated water molecule attacks thepeptide bond, form

ing a

transient tetrahedral interm

ediate.

3.AspartateY acts as an acid to facilitate breakdownof the tetrahedral

interm

ediate and release of thesplit products by donating a proton to the

newlyform

ed amino group. Subsequent shuttling of the protononAsp X

to Asp Y restores the protease to its initialstate.

�The catalytic properties of

enzymes,

and

consequently

their activity, are influenced

by

numerous factors, which all have tobe optimized

and controlled if activity m

easurementsare to be

carried out in a useful andreproducible fashion.

These factors include:

-Physical quantities (temperature, pressure)

-The chemical properties of the solution (pHvalue, ionic

strength),

-The concentrationsof the relevant substrates,

cofactors, and inhibitors.

pH and temperature dependency of enzyme activity

pH and temperature dependency of enzyme activity

Substrate specificity

Substrate specificity

Bisubstrate

Bisubstrate

kinetic

kinetic

Type of inhibition

Type of inhibition

TType of inhibition

ype of inhibition

Kinetic

Kineticof inhibition

of inhibition

Enzyme kinetic as an approach to understand of the mechanism

Coenzyme

Coenzyme

�In m

any enzyme-catalyzed reactions, electronsor groups of atoms

are transferredfrom one substrate to another. This type ofreaction

always also involves additional molecules,whichtemporarily accept

the groupbeing transferred. Helper molecules of thistype are called

coenzymes. As they are notcatalytically active themselves, the less

frequentlyused term

“cosubstrate”would bemore appropriate.

Principal Serum Enzymes Used in Clinical

Principal Serum Enzymes Used in Clinical

Diagnosis.

Diagnosis.

Note: Many of the enzymes are not specific for the disease liste

Note: Many of the enzymes are not specific for the disease listed.

d.

SSome diseases caused by enzyme m

alfunctions

ome diseases caused by enzyme m

alfunctions

33-- m

onooksigenase tyrosine

monooksigenase tyrosine

1,2

1,2-- dioksigenase

dioksigenase homogentisat

homogentisat

Uridilil

Uridililtransferase

transferasegalactosa

galactosa11-- fosfat

fosfat

ββ-- sintase

sintasesintationine

sintationine

44-- m

onooksigenase phenylalanine

monooksigenase phenylalanine

HHeksosaminidase

eksosaminidaseAA

Albino

Albino

Alkaptonuria

Alkaptonuria

GGalactosemia

alactosemia

HHomosistinuria

omosistinuria

ph

phenylketonuria

enylketonuria

TTay

ay-- sachs

sachs

EEnzyme malfunction

nzyme malfunction

diseases

diseases