ENZYMES

ENZYMESENZYMEis a compound, usually a protein, that acts as a catalyst for a biochemical reactionENZYMESThe word enzyme comes from the Greek words en, which means in, and zyme, which means yeast.

Enzymes undergo all the reactions of proteins, including denaturation.ENZYME STRUCTUREA simple enzyme is an enzyme composed only of protein (amino acid chains).

A conjugated enzyme is an enzyme that has a nonprotein part in addition to a protein part.An apoenzyme is the protein part of a conjugated enzyme.A cofactor is the nonprotein part of a conjugated enzyme.ENZYME STRUCTUREA holoenzyme is the biochemically active conjugated enzyme produced from an apoenzyme and a cofactor.

Apoenzyme + Cofactor = Holoenzyme

WHY DO APOENZYMES NEEDS COFACTORS?Cofactors provide additional chemically reactive functional groups besides those present in the amino acid side chains of apoenzymes.

A cofactor is generally either a small organic molecule or an inorganic ion (usually a metal ion).

A coenzyme is a small organic molecule that serves as a cofactor in a conjugated enzyme.Typical inorganic ion cofactors include Zn2+, Mg2+, Mn2+, and Fe2+.

The non metallic ion CI- ion occasionally acts as a cofactor.

Dietary minerals are an important source of inorganic ion cofactors.

Many vitamins have a coenzyme functions in the human body.

NOMENCLATURE AND CLASSIFICATION OF ENZYMESEnzymes are most commonly named by using a system that attempts to provide information about the function (rather than the structure) of the enzyme.

The type of reaction catalyzed and the substrate identity are focal points for the nomenclature.

A substrate is the reactant in an enzyme-catalyzed reaction.Three important aspects of the enzyme-naming process:The suffix ase identifies a substance as an enzyme. The suffix in is still found in some of the first enzymes studied, many of which are digestive enzymes.

TrypsinChymotrypsinPepsinCarbohydraseProteaseLipaseThree important aspects of the enzyme-naming process2. The type of reaction catalyzed by an enzyme is often noted with a prefix.

OxidaseHydrolase

Three important aspects of the enzyme-naming process3. The identity of the substrate is often noted in addition to the type of reactionGlucose oxidasePyruvate carboxylaseSuccinate dehydrogenase

In some cases, only the substrate is given but thenot reaction.UreaseLactase

Six major classes of enzymes base on the type of reaction catalyzedAn oxidoreductase is an enzyme that catalyzes an oxidation-reduction reaction.

2. A tranferase is an enzyme that catalyzes the transfer of a functional group from one molecule to another.

3. A hydrolase is an enzyme that catalyzes a hydrolysis reaction in which the addition of a water molecule to a bond causes the bond to break.

4. A lyase is an enzyme that catalyzes the addition of a group to a double bond or the removal of a group to form a double bond in a manner that does not involve hydrolysis or oxidation.

5. An isomerase is an enzyme that catalyzes the isomerization (rearrangement of atoms) of a substance in a reaction, converting it into a molecule isomeric with itself.

6. A ligase is an enzyme that catalyzes the bonding together of two molecules into one with the participation of ATP.

MODELS OF ENZYME ACTIONENZYME ACTIVE SITEis the relatively small part of an enzymes structure that is actually involved in catalysis.

ENZYME-SUBSTRATE COMPLEX is the intermediate reaction species that is formed when a substrate binds to the active site of an enzyme

LOCK-AND-KEY MODELin the lock-and-key model, the active site in the enzyme has a fixed, rigid geometrical conformation.Only substrates with a complementary geometry can be accommodated at such a site.

Lock-and-Key Model for Enzyme ActivityINDUCED-FIT MODELallows for small changes in the shape or geometry of the active site of an enzyme to accommodate a substrate.

ENZYME SPECIFICITYis the extent to which an enzymes activity is restricted to a specific substrate, a specific group of substrates, a specific type of chemical bond, or a specific type of chemical reaction.

Absolute Specificity the enzyme will catalyze only one reaction. (e.g. Catalase)

Group Specificity the enzyme will act only on molecules that have a specific functional group, such as hydroxyl, amino, or phosphate groups. (e.g. Carboxypeptidase)

Linkage Specificity the enzyme will act on a particular type of chemical bond, irrespective of the rest of the molecular structure. (e.g. Phosphatases)Stereochemical Specificity the enzyme will act on a particular stereoisomer .FACTORS THAT AFFECT ENZYME ACTIVITYENZYME ACTIVITYis a measure of the rate at which an enzyme converts substrate to products in a biochemical reaction.

TEMPERATUREOptimum temperature is the temperature at which an enzyme exhibits maximum activity.

For humans enzymes, the optimum temperature is around 37 degrees Celcius.

The destroying effect of temperature on bacterial enzymes is used in hospital setting to sterilize medical instruments and laundry. In high temperature, high vessels called autoclaves, super-heated steam is used to produce a temperature sufficient to denature bacterial enzymes.

pHOptimum pH is the pH at which enzyme exhibits maximum activityEach enzyme has a characteristic optimum pH, which usually fall within the physiological pH range of 7.0 7.5.Notable exception to this generalization are the digestive enzymes pepsin and trypsin.Pepsin pH 2.0Trypsin pH 8.0SUBSTRATE CONCENTRATIONSaturation curve enzyme activity increases up to a certain substrate concentration and thereafter remains constant.

Turnover number is the number of substrate molecules transformed per minute by one molecule of an enzyme under optimum conditions of temperature, pH, and saturation.

ENZYME CONCENTRATIONIf the amount of substrate present is kept constant and the enzyme concentration is increased, the reaction rate increases because more substrate molecules can be accommodated in a given amount of time. The greater the enzyme concentration, the greater the reaction rate.ExtremoenzymesExtremophile is a microorganism that thrives in extreme environments, environment in which humans and most other forms of life could not survive.acidophiles (3.0 pH or below)alkaliphiles (9.0 pH or above)halophiles (salinity that exceeds 0.2 M NaCL)hypothermophiles (80 122 degrees Celsius)piezophiles (high hydrostatic pressure)cryophiles (15 degrees Celsius or lower)The enzyme present in extremophiles are called extremoenzymes.

Extremoenzymes is a microbial enzyme active at conditions that would inactivate human enzymes as well as enzymes present in other types of higher organisms.

Enzyme InhibitionEnzyme inhibitor is a substance that slows or stops the normal catalytic function of an enzyme by binding to it.

Reversible Competitive InhibitionCompetitive enzyme inhibitor is a molecule that sufficiently resembles an enzyme substrate in shape and charge distribution that it can compete with the substrate for occupancy of the enzymes active site.Reversible Noncompetitive InhibitionNoncompetitive enzyme inhibitor is a molecule that decreases enzyme activity by binding to a site on an enzyme other than the active site.

Irreversible InhibitionIrreversible enzyme inhibitor is a molecule that inactivates enzymes by forming a strong covalent bond to an amino acid side-chain group at the enzymes active site.

Regulation of Enzyme ActivityRegulation of enzyme activity within a cell is a necessity for many reasons.A cell that continually produces large amounts of an enzyme for which substrate concentration is always very low is wasting energy. The production of the enzyme needs to be turned off.A product of an enzyme-catalyzed reaction that is present in plentiful amounts in a cell is a waste of energy if the enzyme continues to catalyze the reaction that produces the product. The enzyme needs to be turned off.Allosteric Enzyme is an enzyme with two or more protein chains (quaternary structure) and two kind of binding sites (substrate and regulator).

Characteristics of allosteric enzymes:Have quaternary structure (composed of two or more protein chainsHave two kinds of binding sites (for substrates and for regulators)Active and regulatory binding sites are distinct from each other in both location and shapeBinding of a molecule in the regulatory site causes changes in the overall three-dimensional structure of the enzyme, including structural changes at the active site

Allosteric EnzymesRegulators substances that bind at the regulatory sites of an allosteric enzyme.

The binding site of a positive regulator increases enzyme activity; the shape of the active site is changed such that it can more readily accept substrate.

The binding site of a negative regulator decreases enzyme activity; changes to the active site are such that substrate is less readily accepted.

Positive and Negative Allosteric ControlFeedback Controlis the process in which activation or inhibition of the first reaction in a reaction sequence is controlled by a product of the reaction sequence.

As illustrative of the feedback control mechanism, consider a biochemical process within a cell that occurs in several steps, each step catalyzed by a different enzyme. The product of each step is the substrate for the next enzyme.3 mechanisms are considered in which enzyme within a cell can be turned on or turned off

Proteolytic Enzymes and ZymogensProteolytic enzyme is an enzyme that catalyzes the breaking of peptide bonds that maintain the primary structure of an enzyme.Zymogen is an inactive precursor of a proteolytic enzyme.

Covalent modification is a process in which enzyme activity is altered by covalently modifying the structure of the enzyme through attachment of a chemical group to or removal of a chemical group from a particular amino acid within the enzymes structure.Covalent Modification of EnzymesThe most commonly encountered type of covalent modification involves the process by which a phosphate group is added to or removed from an enzyme. The source of the added phosphate group is often an ATP molecule. The process of addition of the phosphate group to the enzyme is called phosphorylation, and the removal of the phosphate group from the enzyme is called dephosphorylation.

This two processes are the off/on or on/off switch for the enzyme.The preceding covalent modification processes are governed by other enzymes.Protein kinases effect the addition of phosphate groupsPhophatases catalyze the removal of the phosphate groupsUsually, the phosphate group is added to (or removed from) the R group of a serine, tyrosine, or threonine amino acid residue present in protein. The R groups of these three amino acid have a common structural feature, the presence of a tree OH group. The hydroxyl group is the site where phosphorylation or dephosphorylation occurs.

Prescription Drugs That Inhibit Enzyme ActivityACE INHIBITORS

ACE stands for angiotensin-converting enzyme.

Angiotensin is an octapeptide hormone involve in blood pressure regulation. It increases blood pressure by narrowing blood vessels. Until neeeded, angiotensin is present in the body in an inactive form as the zymogen angiotensinogen, which is a decapeptide.

ACE converts the inactive decapeptide zymogen to the active octapeptide form (angiotensin) by cleaving two amino acids from the zymogen structure.

Ace inhibitor medications block the action of ACE in converting angiotensinogen to angiotensin. The effect of this is a lower blood pressure than if the zymogen activation had occurred.SULFA DRUGSantibiotics is a substance that kills bacteria or inhibits their growth.

Sulfanilamide inhibits bacterial growth because it is structurally similar to PABA (p-aminobenzoic acid).Many bacteria need PABA in order to produce an important coenzyme, folic acid. Sulfanilamide acts as a competitive inhibitor to enzymes in the biosynthesis pathway for converting PABA into folic acid in these bacteria. Folic acid deficiency retards growth of the bacteria and can eventually kill them.PENICILLINSPenicillins inhibit transpeptidase, an enzyme that catalyzes the formation of peptide across links between polysaccharide strands in bacterial cell walls. These cross links strengthen cell walls. A strong cell wall is necessary to protect the bacterium form lysis (breaking open). By inhibiting transpeptidase, penicillin prevents the formation of a strong cell wall. Any osmotic or mechanical shock then causes lysis, killing the bacterium.FOOD-ENZYME INTERACTIONS THAT AFFECT PRESCRIPTION METHOD

Cytochrome P450 liver enzymes involved in the process by which many prescription medications are metabolized in the body.

The most well-known and most studied of the unknown food-enzyme-drug-interactions involves grapefruit, and grapefruit juice, an interaction which is now called the grapefruit effect.Medical Uses of EnzymesEnzymes can be used to diagnose certain diseases. Although blood serum contains many enzymes, some enzymes are not normally found in the blood but are produced only inside cells of certain organs and tissues. The appearance of these enzymes in the blood often indicates that there is tissue damage in an organ and that cellular content are spilling out into the bloodstream.Enzymes can also be used in the treatment of diseases. A recent advance in treating heart attacks is the use of tissue plasminogen activator (TPA), which activates the enzyme plasminogen. When so activated, this enzyme dissolves blood clots in the heart and often provides immediate relief.Selected Blood Enzyme Assays Used In Diagnostic Medicine

Another medical use for enzymes is in clinical laboratory chemical analysis. For example, no simple direct test for the measurement of urea in the blood is available. However, if the urea in the blood is converted to ammonia via the enzyme urease, the ammonia produced, which is easily measured, becomes an indicator of urea.

Blood urea nitrogen (BUN) test is a common clinical laboratory procedure. High urea levels in the blood indicate kidney malfunction.