Transcript Lect2(Enzim

LECTURE 2:
ENZYME
Ribonuclease structure
showing histidine probes
Enzymes are critical for every aspect of cellular
life
What is an important enzyme that you are
familiar with?
PAPAIN
 What is papain?
 Papain is a protein-cleaving
enzyme derived from papaya
and certain other plants.
Enzymes are complex
molecules produced in living
organisms to catalyze (speed
up) chemical reactions within
the cell
PAPAIN
 Why is meat tough?
 Muscles have to endure a lot of mechanical stress; they are
made of strong fibers that make them hard to cut, and tough
connective tissue holds them together. Individual muscle cells
contain microscopic fibrils that give them their structural
integrity and allow them to contract. The fibrils have a
complex internal structure bound together by long protein
chains. The connective tissue that holds the muscle together
is also mostly protein.
 How does papain tenderize meat?
 Papain cuts the protein chains in the fibrils and also in the
connective tissue, disrupting the structural integrity of the
muscle fiber, and tenderizing the meat.
1. DEFINITION
ENZYMES ARE METABLOLIC CATALYSTS.
Enzymes (in yeast) are the largest and most
highly specialized catalysts in the body for the
reactions involved in metabolism which
increase the rate of chemical reactions by
lowering the activation energy of that reactions
ENZYME TOPICS
1.
2.
3.
4.
5.
Functional Properties
Nomenclature
Enzyme Specificity
Enzyme Regulation
Activation Energy
1. Enzyme Properties
ENZYMES ARE
1. Proteins (note that recent developments indicate that both
2.
3.
4.
5.
6.
7.
RNA and antibodies may have catalytic activity, these are
called ribozymes, and catalytic antibodies or abzymes,
respectively)
Biological catalysts, critical components of cell metabolism &
biological processes.
Very efficient catalysts
Reduce G for reaction (by binding the transition state)
Subject to regulatory control of various sorts
Carry out catalysis in a special region of the molecule, the
active-site
Exhibit special kinetics
Very efficient catalysts
A very small quantity of an enzyme can catalyze the
transformation of vastly lager quantity of the substrate

Sucrase (invertase) can effect the hydrolysis of at least
1,000,000 times its own weight of sucrose without
exhibiting any appreciable diminution in its activity
 Catalase is one of the more efficient enzymes, one
molecule of this enzyme being able to catalyze the
conversion 5,000,000 molecules of H202 per minute (the
reduction of hydrogen peroxide to water and molecular
oxygen) when conditions are favorable
THE HYDROLISIS OF SUCROSE CATALYZED BY SUCRASE

Kecepatan reaksi sederhana hidrasi karbon
dioksida meningkat 107 kali lipat dengan enzim
Carbonic anhydrase dibadingkan dengan tanpa
enzim
CO2 + H2O
H2CO3
Setiap molekul Carbonic anhydrase dapat
menghidrasi 105 molekul CO2 per detik

Kecepatan reaksi dengan




hexokinase 1010
phosphorylase 3.1011
alcohol dehydrogenase 2.108
creatine kinase 104.
Enzymatic catalysts have much higher rates than non-enzymatic
catalysts do, and even at relatively low temperatures (Table 1)
UREA FERTILIZER
 The optimum conditions for enzyme catalysis are almost invariably
moderate temperatures, and pHs which are not extreme
 The contrast between a reaction catalysed by an enzyme and by a nonenzymatic catalyst is well illustrated by the process of nitrogen fixation (i.e.
reduction of N2 to ammonia). Nitrogenase catalyses this reaction at
temperatures around 300 K and at neutral pH. The enzyme is a complex
system comprising two dissociating protein components one of which
contains iron and the other iron and molybdenum. Several molecules of
ATP are hydrolyzed during the reduction
 By contrast, in the industrial synthesis of ammonia from nitrogen and
hydrogen, the conditions used are as follows: temperature 700 - 900 K,
pressure 100 - 900 atmospheres, and the presence of an iron catalyst, often
promoted by traces of oxides of other metals
2. Enzyme Nomenclature
Superfamilies: EC 1.1.3.4
 Transferases
 Transfer functional groups between molecules
 Oxidoreductases
 Transfer electrons (RedOx reactions)
 Hydrolases
 Break bonds by adding H2O
 Lyases
 Elimination reactions to form double bonds
 Isomerases
 Intramolecular rearangements
 Ligases
 Join molecules with new bonds
Enzyme Nomenclature
3. Enzyme Specificity
The active site of an enzyme dictates specificity
 Tend to be specific for one type of chemical group
 Substrates have to interact in stereospecific manner (fit)
 Substrates have to bind relatively well (affinity)
 H-bonds, electrostatics, hydrophobicity
 Substrates have to react
 bonds to be broken or formed have to have proper reactivity
 Substances that fit and bind but don’t react are inhibitors
Stereospecificity of Enzymes
The specificity of enzymes for reactions is high different from
inorganic catalysts.
1.
Each enzyme catalyzes only one type of reaction, and
in some cases will limit its activity to only one
particular type of reactant molecule
Incomparison, platinum catalyzes several different
types of reactions.
Enzim proteolitik, sebagai contoh, mengkatalisis hidrolisis
ikatan peptida. Kebanyakan enzim proteolitik juga
mengkatalisis reaksi yang berbeda tapi berhubungan yaitu
hidrolisis ikatan ester
Gambar 1. Hidrolisis ikatan peptida dan ester
2.
Different end products are formed from the same
substrate under the influence of different enzymes.


The trisaccharide raffinose is hydrolized into melibiose
and fructose in the presence of sucrase, while, the end
products of the reaction are sucrose and galactose in the
presence of emulsin
Pyruvic acid is notable for the large number of
compounds into which it may be converted by the action
of different enzymes
Sebagian enzim disintesis dalam bentuk yang
tidak aktif, dan dikatifkan kemudian pada
waktu dan tempat yang tepat secara fisiologi
3.


This regulation is effected through changes in the
catalytic activity of early enzymes in the pathway,
carbamoyl-phosphate synthetase and aspartate
carbamoyltransferase
Enzim pencernaan seperti trypsinogen disintesis dalam
pankreas dan diaktifkan oleh pemotongan ikatan
peptida dalam usus (intestine) kecil untuk membentuk
enzim aktif trypsin
4. The phenomenon of feedback
inhibition is common in many
biosynthetic pathways.

In the biosynthetic pathway leading to the
synthesis of pyrimidine nucleotidcs, the end
products UTP and CTP (=Sitidintrifosfat) are able
to inhibit the first enzyme in the pathway; thus
they are able to limit the flow of metabolites into
that pathway and so regulate their own
biosynthesis
Enzyme Active Sites
 The active site is the specific area of the enzyme to
which the substrate attaches during the reaction
 The active site is part of the conformation of the enzyme
molecule arranged to create a special pocket or cleft
whose three-dimensional structure is complementary to
the structure of the substrate
 The enzyme and the substrate molecules "recognize"
each other through this structural complementarity
 The substrate binds to the enzyme through relatively
weak forces -H bonds, ionic bonds (salt bridges), and van
der Waals interactions between sterically complementary
clusters of atoms.
Lysozyme active site: Green shows
substrate contacts and orange are
catalytic residues
Active site complements structure of
substrate
Contain amino acids that function in
substrate binding, chemical catalysis,
and product release
Enzyme Three Dimensional Structure
 X-ray crystallography (also NMR);
physical methods to solve structure
of enzymes
 Conformation with or without
substrate provides functional/
biological information
 Used to identify amino acids
involved in catalysis
• Example: Prostaglandin Synthase I with
arachidonic acid
• PGHS (COX) target of aspirin
Enzyme Three Dimensional Structure
4. Enzyme Regulation
 Enzymes are tightly regulated light switches
 Unregulated enzymes become constitutively active or
inactive (light is always on or off)
 Unregulated enzyme activity disrupts cell homeostasis and
often lead to disease states.
5. Energi Aktivasi
Kecepatan reaksi yang tinggi dengan keberadaan
enzim berhubungan dengan energi aktivasi
1.

Jika reaksi yang terjadi dalam sel berlangsung diluar
sel, kecepatannya akan sangat lambat kecuali energi
diberikan, misalnya dengan peningkatan suhu.
Sementara reaksi dalam sel berlangsung pada suhu
sekitar lingkungannya (mis. 5o - 40oC).
ACTIVATION ENERGY
2.
Kecepatan reaksi kimia yang tinggi pada suhu
kamar (mis. laboratorium) tidak mungkin terjadi

Karena kebanyakan reaksi kimia, sekalipun
mengeluarkan energi, tidak terjadi secara spontan
(berlangsung dengan sendirinya) tetapi
membutuhkan tambahan energi yang disebut energi
aktivasi (energy of activation).
QUIZ
1.
2.
3.
4.
5.
6.
7.
8.
9.
Define metabolism and anabolic and catabolic reactions
Identify the parts of an enzymes catalyze reactions
Describe method by which enzymes catalyze reactions
Explain the lock-and-key and induced fit models of enzyme action
Explain how changes in pH and temperature will affect enzyme
activity
Define vitamin, and explain why vitamins are essential for normal
cellular function
Describe the function of hormones in the living organism
Define multienzyme system, and explain how such systems are
regulated
Describe the ways in which enzyme activity can be inhibited, and give
examples of each type of inhibition