Enzymes Reaction

Dr. Yogi P. R.

Biochemistry Department

Medical Faculty

Swadaya Gunung Jati University

Cirebon 2009

Tujuan pembelajaran

Untuk memahami dan mampu menjelaskan

1.Pengertian, karakteristik, dan klasifikasi enzim

2.Fungsi Enzim dalam regulasi reaksi kimia tubuh

3.Faktor-faktor yang mempengaruhi kecepatan reaksi enzim dan regulasi aktifitas enzim

4.Fungsi intraseluler melalui regulasi enzim

DEFINITION & CHARACTERISTIC

Enzymes are :

- Proteins

- Metabolic catalysts

- 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

- Unchanged number of enzyme before and after reaction

E : Enzymes ES : Enzymes+Substrates

S : Substrates P : Product

ES low stability

Enzyme Function

LOWERING ACTIVATION ENERGY

9Menurunkan energi)

THE FUNCTION OF CATALYST

ENZYME IS A BIOCATALYSTENZYME IS A BIOCATALYST

Site of activity

A. Endoenzyme

Intracellular enzyme : ATP synthesis

B. Eksoenzyme

Extracellular enzyme

Catalysts effort

Occurred process

A. Constitutive enzyme

The number of enzyme always constant, not influence by substrate concentration (tdk berpengaruh olh cubstrat)

B. Adaptive enzyme

The occurred process is stimulated by substrate

STRUCTURE OF ENZYMES

Cofactor :• Prostetic group• Coenzyme• Activator

COFACTOR COENZYMES

Thiamine pyrophosphate, from Vit. B1, Decarboxylase

Flavin mono/adenine di nuceotide, Vit. B2, Dehydrogenase

Nicatinamide Adenine Dinucleotide/ Phosphate, Nicotinic acid, Dehydrogenase

Coenzyme A, Panthotenic acid, Dehydrogenase

Pyridoxal phosphate, Vit. B6, Transferase

Tetrahydrofolic, Folic acid, Transferase

Deoxyadenosylcobalamine, Vit. B12, Isomerase

COFACTORS ACTIVATOR

Fe2+ or Fe3

+ in Cytochrome oxidase, Catalase and Peroxidase

Co in DinitrogenaseK+ in Pyruvate kinaseMg+ in Glucose 6-phosphatase

Interaction Enzyme-Substrates Model

Lock and key (1890 – Emil Fischer)

Stereospecificity catalysts

The shape, or configuration, of the active site is especially designed for the specific substrate involved

The configuration is determined by the amino acid sequence of the enzyme, the native configuration of the entire enzyme molecule must be intact for the active site to have the correct configuration

The substrate then fits into the active site of the enzyme in much the same way as a key fits into a lock

Induced fit (Daniel Koshland)

The binding of a substrate (S) by an enzyme is an interactive process

The shape of the enzyme's active site is actually modified upon binding S, in a process of dynamic recognition between enzyme and substrate called induced fit

In essence, substrate binding alters the conformation of the protein, so that the protein and the substrate "fit" each other more precisely

Specificity Level of Enzymes

1. Bond specificity (Low specificity)

peptidase, phosphatase, esterase

2. Group specificity (Middle specificity)

hexokinase

3. Absolute specificity (High specificity)

urease

Velocity, Enzymes, Substrates

Acceleration of product is determined by enzyme concentration and substrates concentration

V = Velocity

[E] = Enzyme concentration

[S] = Substrates concentration

A.If the S is CONSTANT The increase of V is equal with the increase of E

B.If the E is CONSTANT and S increase V will increase proportionally with the increase of S, but in higher concentration of S, the increasing of V will decrease slowly until V was almost not suspended from S

A. B.

Michaelis – Menten Model

Leonor Michaelis & Maud Menten -1913

Konstanta Michaelis-Menten Km = k2+k3/k1

Km = The substrate at wich the velocity of the reaction is half the maximum velocity

Km ↓ -- enzyme substrate complex high affinity

Km ↑ -- enzyme substrate complex low affinity

Factors that influence enzymatic reaction

1. Substrates

↑ the substrates concentration will ↑ enzymatic reaction until maximum condition

2. pH

optimum pH will ↑ enzymatic reaction

example : Amilase -- optimum pH 5,0

Arginase -- optimum pH 10

Rat

e of

Rea

ctio

n

Substrate Concentration

Substrate Concentration

Active sites full- maximum turnover

Rat

e of

Rea

ctio

n

pH

1 3 42 5 6 7 8 9

Narrow pH optima

Disrupt Ionic bonds - Structure

Effect charged residues at activesite

3. Temperature

optimum temp will ↑ enzymatic reaction

higher than optimum temp will damage enzyme (± 50C)

If you heat the protein above its optimal temperature bonds break meaning the protein loses it

secondary and tertiary structure

Effect of heat on enzyme activty

Denaturing the protein

ACTIVE SITE CHANGES SHAPE SO SUBSTRATE NO LONGER FITS

Even if temperature lowered – enzyme can’t regain its correct shape

4. Inhibitor

Competitive inhibitor

Another substance (analog substrates) has similar structure to substrate

Succinate Fumarate

These compete with the substrate molecules for the active site

Always reversible

Increasing substrate concentration to against competitor

Succinate Dehydrogenase

Malonate

Non-Competitive inhibitor

These are not influenced by the concentration of the substrate

It inhibits by binding irreversibly to the enzyme but not at the active site

Examples

Cyanide combines with the Iron in the enzymes cytochrome oxidase

Heavy metals, Ag or Hg, combine with –SH groups.

Feed-back inhibitor

The first step (controlled by eA) is often controlled by the end product (F)

Therefore negative feedback is possible

A B C D E F

The end products are controlling their own rate of production

eFeDeCeA eB

Inhibition

© 2008 Paul Billiet ODWS

Alosteric inhibitor

These enzymes have two receptor sites

One site fits the substrate like other enzymes

The other site fits an inhibitor molecule

Inhibitor fits into allosteric site

Substratecannot fit into the active site

Inhibitor molecule

Five Main Ways that Enzyme Activity is Controlled in The Cell

1. Enzyme production (transcription and translation of enzyme genes) enhanced or diminished by a cell in response to changes in the cell's environment

This form of gene regulation is called enzyme induction and inhibition. For example, bacteria may become resistant to antibiotics such as penicillin because enzymes called beta-lactamases are induced that hydrolyse the crucial beta-lactam ring within the penicillin molecule

2. Enzymes can be compartmentalized, with different metabolic pathways occurring in different cellular compartments

For example, fatty acids are synthesized by one set of enzymes in the cytosol, endoplasmic reticulum and the Golgi apparatus and used by a different set of enzymes as a source of energy in the mitochondrion, through β-oxidation

3. Enzymes can be regulated by inhibitors and activators

This helps allocate materials and energy economically, and prevents the manufacture of excess end products. The control of enzymatic action helps to maintain a stable internal environment in living organisms

4. Some enzymes may become activated when localized to a different environment (eg. from a reducing (cytoplasm) to an oxidising (periplasm) environment, high pH to low pH etc).

For example, hemagglutinin in the influenza virus is activated by a conformational change caused by the acidic conditions, these occur when it is taken up inside its host cell and enters the lysosome

5. Enzymes can be regulated through post-translational modification.

For example, in the response to insulin, the phosphorylation of multiple enzymes, including glycogen synthase, helps control the synthesis or degradation of glycogen and allows the cell to respond to changes in blood sugar

Another example of post-translational modification is Chymotrypsin, a digestive protease, is produced in inactive form as chymotrypsinogen in the pancreas and transported in this form to the stomach where it is activated. This stops the enzyme from digesting the pancreas or other tissues before it enters the gut. This type of inactive precursor to an enzyme is known as a zymogen.

Thanks

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Thanks

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