enzymes reaction
Post on 25-Dec-2015
224 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
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
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
…
Thanks
…
top related