Enzymes (A Pharmacologic Approach)

The Pharmacologic Approach to Biological

Catalytic Systems

ENZYMES

Enzymes – biological catalystsCatalysts – (specifically positive* catalysts) are substances that increase the speed of a chemical reaction

Not permanently changed Don’t cause the reaction to

occur Not used up in chemical

reactions so they can be used over and over again

Overview of Enzymes

Enzymes – are organic catalysts produced by living organisms. The reactant in an enzyme-catalyzed reaction is called the “substrate”.

Overview of Enzymes

The small portion of the molecule that is responsible for the catalytic action of the enzyme is the “active site”.

Overview of Enzymes

Enzymes are superior to other catalysts in several ways:

1. They have a much greater catalytic power.

CO2 + H2O carbonic anhydrase H2CO3

Overview of Enzymes

2. Enzymes are highly specific with varying degrees of specifity.

Absolute specificity – they act on one substrate and only on that substrate

Stereospecificity – such enzymes that can detect the difference between optical isomers (mirror

images) and select only one of such isomers

Overview of Enzymes

Reaction specificity – enzymes that catalyze certain types of reactions

Group specificity – enzymes that catalyzes a group of substances that contain specific compounds.

Overview of Enzymes

3. The activity of enzymes is closely regulated, whereas catalyst activity is difficult to control.

[Most] Enzymes are proteins and therefore undergo all the reactions that proteins do. That is, enzymes can be coagulated by heat, alcohol, strong acids, and alkaloidal reagents.

Enzyme Reaction

Major Factors affecting Enzymatic Reactions:

(1) Temperature (2) pH (3) Substrate Concentration(4) Availability of Catalyzing Enzymes

Enzyme Reaction

Temperature Requirement

The higher the temperature, the faster the rate of reaction. The best temperature for enzyme function – the temperature at which the rate of a reaction involving an enzyme is the greatest – is called the “optimum temperature”.

Enzyme Reaction

Enzyme ReactionRole of pH

Each enzyme has a pH range within which it can best function. This is called “optimum pH range” for that particular enzyme. For example, the optimum pH range of pepsin, an enzyme found in gastric juice, is approximately 2.0, whereas the optimum pH range of trypsin, an enzyme found in pancreatic juice, is near 8.2.

Enzyme ReactionRole of pH

If the pH of a substrate is too far from the optimum pH required by the enzyme, that enzyme cannot function at all. However, since body fluids contain buffers, the pH usually does not vary too far from the optimum values.

Enzyme ReactionEffect of Substrate Concentration

As with the all chemical reactions, the rate of formation is increased with an increase in concentration of reactants. With an increased concentration of substrate, the speed of the reaction will increase until all available enzymes becomes saturated with substrate.

Enzyme ReactionImpact of Enzyme Availability

With an increase in the amount of enzyme, the rate of reaction will increase, assuming an unlimited supply of substrate.

Activators and InhibitorsActivators/ Inducers – inorganic or organic

substances that tend to increase the activity of an enzyme.Inhibitors – any substance that will make the enzyme less active or render it totally inactive.

Activators and InhibitorsTypes of Enzyme Inhibitors:

Competitive/ Reversible inhibitors – bind reversibly to the active site, blocking the access by the substrate.Noncompetitive inhibitors – bind to another site (the allosteric site) on the enzyme to render it less active or inactive.

Activators and InhibitorsTypes of Enzyme Inhibitors:

Irreversible inhibitors – form strong covalent bonds with the enzymes, rendering it inactive. This effect cannot be overcome by increasing the concentration of the substrate.

Activators and InhibitorsPoisons

Many enzymes inhibitor are poisonous because of their effect on enzyme activity. Mercury and Lead compounds are poisonous because they react with sulfhydryl groups ( - SH) of enzymes and change their conformation. The subsequent loss of enzyme activity leads to the various symptoms of lead and mercury poisoning, such as loss of equilibrium, hearing, sight, and touch, which are generally irreversible.

Activators and InhibitorsDrugs

While some enzyme inhibitors are poisonous, others are beneficial to life. Penicillin acts as an enzyme inhibitor for transpeptidase, the very enzyme that bacteria require to build their cell walls. If the cell wall is lacking, osmotic pressure causes the bacterial cell to burst and die.

Activators and InhibitorsDrugs

However, new strains of bacteria have developed an enzyme, penicillinase, that inactivates penicillin. To destroy these new strains, synthetically modified penicillins have been prepared so that this antibiotic remains effective.

Mode of Enzyme Activity


Lock-and-Key ModelWherein the substrate must “fit” into the

active site of the enzyme – hence the specificity of the enzyme.

Induced-Fit ModelSuggests that the active site is not rigid as the

Lock-and-Key Model, but flexible. That is, the site changes in conformation upon binding to a substrate in order to yield an enzyme-substrate fit.


Some enzymes are conjugated proteins – they contain a protein and non-protein part. Both parts must be present before the enzyme can function.

The protein part is called the “apoenzyme” and the non-protein (organic) is called “coenzyme”.

Sometimes, enzymes require a metal ion activator to function called a “prosthetic group”.

The Holoenzyme

Coenzymesare not proteins and so are not inactivated by

heat. Examples of coenzymes are the vitamins or compounds derived from vitamins. The reaction involving a coenzyme can be written as follows:

coenzyme + apoenzyme = holoenzyme

Coenzyme A is essential in the metabolism of carbohydrates, lipids, and proteins in the body.

The Holoenzyme

active (whole enzyme)inactive

Enzyme NomenclatureFormerly enzymes were given names ending

in “-in”. With no relation being an indicator between the enzyme and the substance it affects – the substrate.

The current system for naming enzymes uses the name of the substrate and [more importantly] the type of reaction involved, with the ending “-ase”.

Enzyme NomenclatureE N Z Y M E SUBTRATE or REACTION TYPE

Maltase Maltose

Urease Urea

Proteases Proteins

Carbohydrases Carbohydrates

Lipases Lipids

Hydrolases Hydrolysis Reaction

Deaminases Removing amines

Dehydrogenases Removing hydrogens

Enzyme NomenclatureThe Enzyme Commission number (EC

number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze.

As a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme.

Enzyme NomenclatureStrictly speaking, EC numbers do not specify

enzymes, but enzyme-catalyzed reactions. If different enzymes (for instance from different organisms) catalyze the same reaction, then they receive the same EC number.

Enzyme NomenclatureFurthermore, through convergent evolution,

completely different protein folds can catalyze an identical reaction and therefore would be assigned an identical EC number (these are called non-homologous isofunctional enzymes, or NISE).

By contrast, UniProt identifiers uniquely specify a protein by its amino acid sequence.

Enzyme ClassificationTop-Level Enzyme Commission Numbers

Group Reaction catalyzed Typical reaction ExamplesEC 1

Oxidoreductases

To catalyze oxidation/reduction reactions; transfer of H and O atoms or electrons from one substance to another

AH + B → A + BH (reduced)A + O → AO (oxidized)

Dehydrogenase, oxidase

EC 2Transferase

s

Transfer of a functional group from one substance to another. The group may be methyl-, acyl-, amino- or phosphate group

AB + C → A + BC Transaminase, kinase

EC 3Hydrolases

Formation of two products from a substrate by hydrolysis

AB + H2O → AOH + BH Lipase, amylase, peptidase

Enzyme ClassificationTop-Level Enzyme Commission Numbers

Group Reaction catalyzed Typical reaction ExamplesEC 4

LyasesNon-hydrolytic addition or removal of groups from substrates. C-C, C-N, C-O or C-S bonds may be cleaved

RCOCOOH → RCOH + CO2 or [X-A-B-Y] → [A=B + X-Y]

Decarboxylase

EC 5Isomerases

Intramolecule rearrangement, i.e. isomerization changes within a single molecule

ABC → BCA Isomerase, mutase

EC 6Ligases

Join together two molecules by synthesis of new C-O, C-S, C-N or C-C bonds with simultaneous breakdown of ATP

X + Y+ ATP → XY + ADP + Pi

Synthetase

Oxidoreductases – are enzymes that catalyze oxidation-reduction reactions between two substrates. The enzymes of the oxidation-reduction reactions in the body are important because these reactions are responsible for the production of heat and energy.

Transferases – are enzymes that catalyze the transfer of a functional group between two substrates.

Enzyme Classification

Hydrolases – hydrolytic enzymes – catalyze the hydrolysis of carbohydrates, esters and proteins.

Lyases – are enzymes that catalyze the removal of groups from substrates by means other than hydrolysis, usually with the formation of

double bonds.


Isomerases – are enzymes that catalyze the interconversion of cis-trans isomers.

Ligases – or synthetases, are enzymes that catalyze the coupling of two compounds with breaking of pyrophosphate bonds.


If an individual’s blood pressure drops, as in the case of hemorrhaging or in hypokalemia, the kidneys secrete the enzyme renin (sometimes considered as a hormone) into the bloodstream.

angiotensinogen renin angiotensin I ANG I converting enzyme angiotensin II

Angiotensin II increases the force of the heartbeat and constricts the arterioles, thus causing an increase in blood pressure.

Enzymes of the Kidney

Angiotensin II brings about the contraction of the vascular smooth muscle and also triggers the release of the hormone aldosterone which aids in the retention of water. Actually, angiotensin II is the most powerful vasoconstrictor known. It is an octapeptide; Angiotensin I is a decapeptide.


Other kidney enzymes include glucose-6-phosphatase, which is involved in the removal of the phosphate group from glucose-6-phosphate, thereby enabling glucose to diffuse from the cell into the blood stream;

Glutaminase, which is involved in the conversion of glutamine into glutamic acid and NH4+ ; and a

hydroxylase, which is involved in the synthesis of calcitriol.


Chemotherapy is the use of chemicals to destroy infectious microorganisms and cancerous cells without damaging the host’s cells. These

chemicals function by inhibiting certain cellular enzymatic reactions. Among the chemotherapeutic agents are the antibiotics and the antimetabolites.

Chemotherapy

Antibiotics – are compounds produced by one microorganism that are toxic to another microorganism. Among the most commonly used are the penicillins and tetracyclines.

Chemotherapy

Penicillin

Tetracycline

Chemotherapy

Antimetabolites – are chemicals that have structures closely related to those of the substrate enzymes act on, thus inhibiting enzyme activity.

Mercaptopurine is used in the treatment of leukemias. Some are antibiotics.

Chemotherapy

One of the most promising new chemotherapeutic agent in decades is taxol, a natural product obtained from the bark of Pacific yew trees. Taxol acts by interfering with cellular growth and function and is very effective in shrinking a variety of tumors, particularly in advanced cases of ovarian and breast cancer.

Chemotherapy

The measurement of plasma enzyme levels can be of great diagnostic value. Many other plasma enzymes are useful in the diagnosis of various diseases.

Clinical Significance of Plasma Enzyme Concentrations

SERUM ENZYME MAJOR DIAGNOSTIC USEGlutamate oxaloacetate transaminase

(SGOT)Myocardial Infarction

Glutamate pyruvate transaminase (SGPT) Infectious Hepatitis

Trypsin Acute pancreatic disease

Ceruloplasmin Wilson’s Disease


SERUM ENZYME MAJOR DIAGNOSTIC USE

Amylase Liver and pancreatic disease

Acid phosphate Prostate Cancer

Alkaline phosphatase Liver or bone disease

Creatine phosphokinase Myocardial infarction, muscle disorders

Lactate dehydrogenase Myocardial Infarction, leukemia, anemia

Renin Hypertension


Isozymes or Isoenzymes are enzymes with the same function but

slightly different structural features. The reason for their existence is not unknown, but they are made use of clinically. Lactate dehydrogenase (LDH), creatine kinase, and alkaline phosphatase all occur in isoenzyme forms and are of diagnostic value. LDH has five forms.

Isozymes

Condition Isoenzyme Pattern

Myocardial InfarctionModerate elevation of LDH1;

Slight elevation of LDH2

Acute HepatitisLarge elevation of LDH5;

Moderate elevation of LDH4

Muscular Dystrophy Elevation of LDH1, LDH2, LDH3

Megaloblastic Anemia Large elevation of LDH1

Sickle-cell Anemia Moderate elevation of LDH1, LDH2

Arthritis with Joint effusions Elevation of LDH5

Clinical Significance of the Relative Amount of LDH

Allosteric regulation is the regulation of an enzyme or

other protein by binding an effector molecule at the enzyme's allosteric site (that is, a site other than the active site).

Effectors that enhance the protein's activity are referred to as allosteric binders, whereas those that decrease the protein's activity are called noncompetitive inhibitors.

Allosteric Regulation

Allosteric regulation This control of key enzymes is of utmost

importance to ensure that biologic processes remain coordinated at all times to meet the immediate metabolic needs of the cells.

Allosteric Regulation

Zymogensare inactive precursors of enzymes.

Most digestive and blood-clotting enzymes exist in the zymogen form, until activated.

In the case of digestive enzymes, this is necessary to prevent digestion of pancreatic and gastric tissue. For blood clotting, it is to avoid premature of blood cells.

Zymogens

ZYMOGEN ACTIVE FORM OF ENZYME

pepsinogen pepsin

trypsinogen trypsin

prothrombin thrombin

Zymogens

Lactose IntoleranceIndividuals who cannot eat food

containing lactose are said to be lactose intolerant.They lack the enzyme lactase, which is required for the hydrolysis of lactose.

As a result, lactose accumulates in the intestinal tract and pulls water out of the tissues by osmosis. This is turn causes abdominal cramps, distention, and diarrhea.

Zymogens

Lactose Intolerance

To overcome such an effect today, an individual may take Lactaid® orally to supply the missing enzyme.

Zymogens

DAGHANG SALAMAT SA MGA WALA NAMINAW…

GOD BLESS!

PADAYON sa gibati…

Science

Enzymes (A Pharmacologic Approach)