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•Aceleran la velocidad de las reacciones bioquímicas.
•Específicas para un sustrato.
•Reacciones ocurren en ambiente fisiológico (pH, temperatura y presión).
•Proveen para reacciones acopladas
•Algunas funcionan como puntos de regulación en rutas metabólicas.
EnzimasEnzimas
Fig. 7-10, p. 162
Activation energy (EA) without enzyme
Activation energy (EA) with enzyme
Energy of reactants
Change in free energy (ΔG)
Fre
e en
erg
y (G
)
Energy of products
Progress of reaction
EnzymesEnzymes
Enzyme-Substrate ComplexEnzyme-Substrate Complex
E + S ES E + P
-asa o “-ase”
S Δk1k-1
P
Oxidoreductases
Transferases
En citosol
Hydrolases
Lyases (Synthase)
Isomerases
Ligases
Lysyl oxidase is an extracellular copper enzyme that catalyzes formation of aldehydes from lysine residues in collagen and elastin precursors
Catalasa
Metaloproteasa
Zn++, Fe+++, Cu++ Tóxicos- Cd++, Hg++ por Zn++
The list of enzymes which use zinc as a cofactor are :
1. glutamate dehydrogenase2. alcohol dehydrogenase3. lactate dehydrogenase4. carbonic anhydrase5. alkaline phosphatase6. DNA polymerase7. RNA polymerase8. delta-ALA dehydratase9. superoxide dismutase10. pancreatic carboxypeptidase
Cofactor Vitamin Additional component
Chemical group(s) transferred Distribution
Thiamine pyrophosphate [24]
Thiamine (B1) None 2-carbon groups, α cleavage
Bacteria, archaea and eukaryotes
NAD+ and NADP+ [25] Niacin (B3) ADP Electrons Bacteria, archaea and eukaryotes
Pyridoxal phosphate [26]
Pyridoxine (B6) None Amino and carboxyl groups
Bacteria, archaea and eukaryotes
Lipoamide [3] Lipoic acid None electrons, acyl groupsBacteria, archaea and eukaryotes
Methylcobalamin [27] Vitamin B12 Methyl group acyl groupsBacteria, archaea and eukaryotes
Cobalamine [3] Cobalamine (B12) Nonehydrogen, alkyl groups
Bacteria, archaea and eukaryotes
Biotin [28] Biotin (H) None CO2Bacteria, archaea and eukaryotes
Coenzyme A [29] Pantothenic acid (B5) ADP Acetyl group and other acyl groups
Bacteria, archaea and eukaryotes
Tetrahydrofolic acid [30]
Folic acid (B9) Glutamate residuesMethyl, formyl, methylene and formimino groups
Bacteria, archaea and eukaryotes
Menaquinone [31] Vitamin K None Carbonyl group and electrons
Bacteria, archaea and eukaryotes
Ascorbic acid [32] Vitamin C None Electrons Bacteria, archaea and eukaryotes
Flavin mononucleotide [33]
Riboflavin (B2) None Electrons Bacteria, archaea and eukaryotes
Flavin adenine dinucleotide [33]
Riboflavin (B2) None Electrons Bacteria, archaea and eukaryotes
Coenzyme F420 [34] Riboflavin (B2) Amino acids Electrons Methanogens and some bacteria
Enzymes are used in an increasing number of application areas including:
a) detergents, b) food processing, c) brewing, d) household products, e) manufacture of pharmaceuticals molecules,
f) environmental and clinical assay kits, as
labels in immunological ELISA tests and biosensors.
1,6-Dihydro nicotinamide adenine dinucleotide inhibits both
H-type lactic dehydrogenase and M-type lactic
dehydrogenase which are isoenzymes of lactic
dehydrogenase, but the degree of inhibition thereof against
H-type considerably differs from that against M-type. A ratio
of H-type lactic dehydrogenase to M-type lactic
dehydrogenase in serum can be measured by utilizing the
difference of inhibition degree. Therefore we can diagnose
the organ with trouble.
S P
V = P/t
V = k[S]
k= V/[S]
k
*En solución saturada de sustrato
Vmax = Kcat x [E]total
Kcat = Vmax / [E]total
[E]total= Vmax / Kcat
E + S ES E + Pk1
k-1
k2
Cinética de las Enzimas
K = V/[E]
*En solución saturada de sustrato
Vmax = Kcat x [E]total
Kcat = Vmax / [E]total
[E]total= Vmax / Kcat
Kcat = moles de S convertidos a P por segundo por mol de enzima(en solución saturada)
En solución saturada de sustrato
Kcat = Vmax / [E]total
En solución saturada de sustrato
Vmax = Kcat x [E]total
Kcat = Vmax / [E]total
[E]total= Vmax / Kcat
*En concentración constante de la enzimay no saturada de sustrato
Y= ax
b+x
b = a/2
k2
k-1
k1
E + S ES E + P
Km = k-1/k1 :. Km mayor = menos afinidad Variaciones con las isoenzymas
Michaelis–Mentenequation
Gen5 Data Analysis Software (BioTek Instruments)
Kcat = Vmax / [E]total
[E]total= Vmax / Kcat
InhibitionInhibition
• Reversible inhibitionReversible inhibition • competitivecompetitive (inhibitor competes with substrate (inhibitor competes with substrate
for active site)for active site)• noncompetitivenoncompetitive (inhibitor binds at a different (inhibitor binds at a different
site) site)
• Irreversible inhibitionIrreversible inhibition• inhibitor combines with enzyme and inhibitor combines with enzyme and
permanently inactivates itpermanently inactivates it
Gas nerviosoinhibidor de aceticolinesterasa
Insecticidas con inhibidor de aceticolinesterasa
Inhibidores de aceticolinesterasapara el Alzheimer
•Regulación de las enzimas en metabolismo
•concentración de la enzimas
•concentración del sustrato
•modulaciones alostéricas
•modificaciones covalentes
•cambios en pH
•temperatura
Feedback InhibitionFeedback Inhibition
• End product End product inhibits inhibits earlier earlier reaction in reaction in metabolic metabolic pathwaypathway
Alimentación positiva
Feed-forward activation
Fosforilación (cinasas)
Desfosforilación(fosfatasas)
Zimógenos
Fig. 7-12b, p. 164
Trypsin
Pepsin
pH
(b) Enzyme activity is very sensitive to pH. Pepsin is a protein-digesting enzyme in the very acidic stomach juice. Trypsin, secreted by the pancreas into the slightly basic small intestine, digests polypeptides.
Rat
e o
f re
acti
on
Fig. 7-12a, p. 164
Most human
enzymes
Enzymes of heat-tolerant
bacteria
Rat
e o
f re
acti
on
Temperature (°C)
(a) Generalized curves for the effect of temperature on enzyme activity.
Acid-Base Catalysis
Covalent Catalysis
Animation: Allosteric Animation: Allosteric ActivationActivation
CLICKTO PLAY
Fig. 7-17a, p. 167
Substrate
Inhibitor
Enzyme
(a) Competitive inhibition. The inhibitor competes with the normal substrate for the active site of the enzyme. A competitive inhibitor occupies the active site only temporarily.
Inhibitor binds to active siteSubstrate
Fig. 7-17b, p. 167
Substrates Active site
Inhibitor
(b) Noncompetitive inhibition. The inhibitor binds with the enzyme at a site other than the active site, altering the shape of the enzyme and thereby inactivating it.
Active site not suitable for reception of substratesEnzyme
Animation: Allosteric Animation: Allosteric InhibitionInhibition
CLICKTO PLAY
Animation: Chemical EquilibriumAnimation: Chemical Equilibrium
CLICKTO PLAY
Exergonic ReactionsExergonic Reactions
• have a negative have a negative ΔΔG G valuevalue• free energy decreasesfree energy decreases
• are spontaneousare spontaneous• release free energy that can perform workrelease free energy that can perform work
Endergonic ReactionsEndergonic Reactions
• have a positive have a positive ΔΔG G valuevalue• free energy increasesfree energy increases
• are are notnot spontaneous spontaneous
Fig. 7-3, p. 156
Fig. 7-3a, p. 156
Reactants
Free energy decreases
Fre
e en
erg
y (G
)
Products
Course of reaction
(a) In an exergonic reaction, there is a net loss of free energy. The products have less free energy than was present in the reactants, and the reaction proceeds spontaneously.
Fig. 7-3b, p. 156
Reactants
Free energy increases
Fre
e en
erg
y (G
)
Products
Course of reaction
(b) In an endergonic reaction, there is a net gain of free energy. The products have more free energy than was present in the reactants.
Coupled ReactionCoupled Reaction
• Input of free energy required to drive an Input of free energy required to drive an endergonic reaction endergonic reaction is supplied by an is supplied by an exergonic reactionexergonic reaction
A→A→B B ΔΔG = +20.9 kJ/molG = +20.9 kJ/mol
C→C→D D ΔΔG = -33.5 kJ/molG = -33.5 kJ/mol
Overall Overall ΔΔG = -12.6 kJ/molG = -12.6 kJ/mol
Learning Objective 9Learning Objective 9
• How can an How can an enzymeenzyme lower the required lower the required energy of activationenergy of activation for a reaction? for a reaction?
ATP and ADPATP and ADP
Catabolism and AnabolismCatabolism and Anabolism
• CatabolismCatabolism• degradation of large complex molecules into degradation of large complex molecules into
smaller, simpler moleculessmaller, simpler molecules• exergonicexergonic
• AnabolismAnabolism• synthesis of complex molecules from simpler synthesis of complex molecules from simpler
moleculesmolecules• endergonicendergonic
ATP Links Exergonic and ATP Links Exergonic and Endergonic ReactionsEndergonic Reactions
NAD+ and NADHNAD+ and NADH
Fig. 7-7, p. 160
NAD+ (oxidized) NADH (reduced)
Nicotinamide
Ribose
Phosphate
Adenine
Phosphate
Ribose