Week 8 - Enzymes

Enzymes

A compound, protein that acts as a catalyst for a biochemical reaction; not consumed during the reaction but helps the reaction occur more rapidly

Simple Enzyme

Composed of only a protein

Conjugated Protein

Has a non-protein part in addition to a protein part

Apoenzyme

Protein for Conjugated Enzyme

Cofactor

Non-protein part of the conjugated enzyme

Holoenzyme

Biochemically active conjugated enzyme produced from an apoenzyme and a cofactor

Coenzyme

Serves as a cofactor in a conjugated enzyme

Substrate

Reactant in an enzyme - catalyzed reaction

Oxidorecductase

Catalyzes an oxidation - Reduction reaction; requires a coenzyme that is oxidized or reduced as the substrate is reduced or oxidized

Transferase

Catalyzes the transfer of a functional group from one molecule to another

Transaminases

Catalyzes the transfer of amino group from one molecule to another

Kinases

Catalyzes the transfer of phosphate group from ATP to give ADP and a phosphorylated product

Hydrolase

Catalyzes the hydrolysis reaction; central to process of digestion

Carbohydrases, Proteases, Lipases

Hydrolase examples (3)

Lyase

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

Isomerase

Catalyzes the isomerization of a substrate in a reaction converting it to a molecule isomeric with itself; One reactant and one product in reactions

Ligase

Catalyzes the bonding together of two molecules into one with the participation of ATP

Enzyme active site

Small part of an enzyme's structure that is actually involved in catalysis; 3D entity formed by groups that come from different parts of the proteins chains

Enzyme substrate complex

The intermediate reaction species that is formed when a substrate binds to the active site of an enzyme

Lock and Key model

Active site in the enzyme has the fixed, rigid, geometrical conformation; Substrate with a complementary geometry can be accommodated

Induced Fit model

Enzyme's active site is not rigid and static; constant shape; Allows for changes in the shape or geometry of the active site of an enzyme to accommodate a substrate; Adapts the incoming substrate

Enzyme Specificity

Enzyme's activity is restricted to a specific substrate, a specific group of substrate, a specific type of chemical bond, or a specific type of reaction

Absolute Specificity

Catalyzes only one reaction; most restrictive of all specificities

Group Specificity

Act only on molecules that have a specific functional group, such a hydroxyl, amino or phosphate groups

Linkage Specificity

Act on the particular type of bond, irrespective to the rest of the molecular structure; Most general of the common species

Phosphatases hydrolyze phosphate

Ester bonds in all types of phosphate esters

Stereochemical Specificity

Act on a particular isomer

Enzyme Activity

Measures the rate at which an enzyme converts substrate to products in a biochemical reaction

Temperature, pH, Substrate Concentration, Enzyme Concentration

Factors that affects enzyme activity

Temperature

Measures kinetic energy of molecules; molecules are moving faster and colliding more frequently because of high temperature

Optimum Temperature

Temperature at which an enzyme exhibits maximum activity

pH

The charge on acidic and basic amino acids located at the active site depends on it; it can result in enzyme denaturation and subsequent loss of catalytic activity

Optimum pH

pH at which an enzyme exhibits maximum activity; it ranges from 7.0 - 7.5

Pepsin

Active in the stomach; functions best at pH 2.0

Trypsin

Operates in the small intestine; functions best at pH 8.0

Substrate Concentration

Increased concentration of substrate will obtain the enzyme activity

Turnover number

Number of substrate molecule transformed per minute by one molecule of enzyme under optimum conditions of temperature, pH and saturation

Enzyme Concentration

Kept in low number because enzymes are not consumed in the reaction; greater the enzyme concentration, the greater the reaction rate

Extremozymes

Microbial enzymes active at a condition that would inactivate human enzymes as well as enzymes present in other types of higher organism

Extremophile

Microorganism that thrives in extreme environments

Acidophiles

Optimal growth at pH levels of 3.0 or below

Alkaliphiles

Optimal growth at pH levels of 9.0 or above

Hyperthermophile

Temperature between 80C and 122C needed to thrive

Halophiles and Cryophiles

Extremozymes

Enzyme Inhibitor

Substance that slows or stops the normal catalytic function of an enzyme by binding to it

Competitive enzyme inhibitor

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 non-competitive inhibition

Molecule that decreases enzyme activity by binding to a site on an enzyme other than the active site; presence of this causes a change in the structure of the enzyme sufficient to prevent the catalytic groups at the active site from affect the catalyzing action/

Irreversible inhibition

Molecule that inactivates enzyme by forming a string covalent bond to an amino acid side - chain group at the enzymes active site

Allosteric Enzyme

2 or more protein chains; 2 kinds of binding sites; Active and regulatory sites are distinct

Regulators

Substance that bind at the regulatory sites of allosteric enzymes

Positive regulator

Increase enzyme activity; shape of the active site is changed that it can readily accept substrate

Negative Regulator

Decrease enzyme activity; changes active site are such that substrate is less readily accepted

Feedback control

Process in which activation or inhibition of the first reaction in a reaction sequence is controlled by a product of a reaction sequence

Proteolytic Enzymes

Catalyzes the breaking of peptide bonds that maintain the primary structure of protein; generated in an inactive form and converted to a active form when they are needed

Zymogen

Inactive precursor of proteolytic enzyme; controlled reaction that moves some part of the structure which then affects the active site conformation

Covalent modification of Enzyme

Enzyme activity altered by covalently modifying the structure of the enzyme through attachment of a chemical group or removal of a chemical group from a particular amino acid within the enzyme structure

Phosphorylation

Process of addition of the phosphate group to the enzyme by protein kinases

Dephosphorylation

Removal of the phosphate group from the enzyme by phosphatases