•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