CHAPTER 3 ENZYMES Leonardus, S.Si.

Mode of action of enzymes Factors that affect enzyme action Content Mode of action of enzymes Factors that affect enzyme action

Learning Outcomes Candidates should be able to: (a) explain that enzymes are globular proteins that catalyse metabolic reactions; (b) explain the mode of action of enzymes in terms of an active site, enzyme/substrate complex, lowering of activation energy and enzyme specificity;

Learning Outcomes (c) [PA] follow the progress of an enzyme-catalysed reaction by measuring rates of formation of products(for example, using catalase) or rates of disappearance of substrate (for example, using amylase); (d) [PA] investigate and explain the effects of temperature, pH, enzyme concentration and substrate concentration on the rate of enzyme-catalysed reactions;

Learning Outcomes (e) explain the effects of competitive and non-competitive inhibitors on the rate of enzyme activity; (f) use the knowledge gained in this section in new situations or to solve related problems.

Introduction Enzyme name is usually end in –ase eg. Amylase, lipase, etc Enzymes are used in several processes such as food manufacture, production of pharmaceuticals and chemicals, analytical methods and medical research Without enzyme most of the reaction inside the cell cannot occur. They don’t change the nature of the products reactions that they catalyse.

Introduction A small amount of enzymes can bring about a lot of substrate to became product. This is because the enzyme is not destroyed by the reaction it catalyse. All enzyme reactions are reversible.

Characteristics of Enzymes Enzymes are globular proteins, which act as catalysts (speed up the metabolic reaction) Enzymes are globular proteins enzyme molecule coiled into a precise 3D structure that hydrophilic R-chain on the outside to make sure enzyme soluble Enzymes can be defined as biological catalysts All enzymes are globular proteins. They dissolve freely in water and function independently in the protoplasm of the cell, outside the cell or attached to the membrane

Characteristics of Enzymes Enzyme are globular proteins Protein

Enzyme are globular proteins Characteristics of Enzymes Enzyme are globular proteins back

Characteristics of Enzymes Enzymes work by lowering the activation energy for the reaction that is catalyzed An uncatalyzed reaction requires a higher activation energy than does a catalyzed reaction There is no difference in free energy between catalyzed and uncatalyzed reactions Activation Energy is the energy required for a reactant or substrate to start a reaction. Enzim mengkatalis reaksi dengan meningkatkan kecepatan reaksi. Meningkatkan kec reaksi dilakukan dgn menurunkan energi aktivasi (energi yg diperlukan utk melakukan reaksi)

Characteristics of Enzymes Activation Energy is the energy required for a reactant or substrate to start a reaction. Enzim mengkatalis reaksi dengan meningkatkan kecepatan reaksi. Meningkatkan kec reaksi dilakukan dgn menurunkan energi aktivasi (energi yg diperlukan utk melakukan reaksi)

Characteristics of Enzymes Each enzyme acts on only one specific substrate, because there has to be a perfect match between the shape of the substrate and the shape of the enzyme’s active site to form an enzyme-substrate complex ex: Hexokinase only acts on all hexoses. Glucokinase only acts on glucose not fructose.

Characteristics of Enzymes Enzymes work specifically

Characteristics of Enzymes Enzymes work specifically

Characteristics of Enzymes Enzymes work specifically Enzyme-substrate complex bind at active site

Enzyme work There are two hypotheses have been put forward to explain enzyme activity: Lock-and-key hypotheses Induced-fit hypotheses

Lock-and-key hypotheses Enzyme work Lock-and-key hypotheses Proposed by Emil Fischer (1890) Theory: enzyme had a particular shape into which the substrate(s) fit exactly. i.o.w. the shape of the substrate is complementary to the shape of the active site of the enzyme Substrate=key, enzyme=lock i.o.w. : in other words

Enzyme work

Enzyme work Induced-fit hypotheses Proposed by Daniel Koshland (1959) Theory: the initial shape of the active site of an enzyme might not be complementary to the shape of the substrate. Binding of the substrate to the active site induces a conformational change in the shape of the enzyme, which enables the substrate to fit more snugly into the active site. i.o.w. the active site has a shape complementary to that of the substrate only after the substrate is bound Active site=flexible After product getting loose, the active site back at first i.o.w. : in other words Induce: membujuk Snugly: pas

Enzyme work

Enzyme work Lock-and-key and induced fit model

Enzyme activity The activity of an enzyme is the measure of how well it catalyses its specific Factors affecting enzyme activity : Enzyme concentration Substrate concentration Temperature pH Presence of inhibitors

1. Enzyme concentration Enzyme activity The active site can be reused for several times, unless the substrate is limited, the rate of reaction will increase linear by increasing amount of enzyme

2. Substrate concentration Enzyme activity 2. Substrate concentration At lower substrate concentration, some enzyme molecules have their active site “free” When substrate is increased then the all active sites of enzyme molecules are “occupied” Vmax is the rate of enzyme catalyzed reaction when all active site are saturated with substrate Vmax

3. Temperature Enzyme activity 3 Rate Of Reaction 2 4 1 0 10 20 30 40 50 Rate Of Reaction Temperature/oC 3 4 1 2 At low temperatures, the reaction takes place only very slowly As temperature continues to increase, the speed of movement of the substrat and enzyme molecules also continues to increase The temperature at which an enzyme catalyses a reaction at the maximum rate is called the optimum temperature, at about 37-400C At high temperature, enzyme loses the catalytic ability, known as denaturation (irreversible)

Optimal temperature of thermophilic bacteria Enzyme activity Optimal temperature of thermophilic bacteria

4. pH (potential hydrogen) Enzyme activity 4. pH (potential hydrogen) Enzymes prefer to work at an optimum pH. Outside of its can cause denaturation of an enzyme Most enzymes work fastest at a pH of somewhere around 7 However, such as the protease, pepsin, which is found in the acidic condition of the stomach, have different optimum pH pepsin amylase Optimum pH Rate Of Reaction 1 2 3 4 5 6 7 8 9 10 pH

Optimal pH of some enzymes Enzyme activity Optimal pH of some enzymes

Optimal pH of some enzymes Enzyme activity Optimal pH of some enzymes

5. Presence of Inhibitors Enzyme activity 5. Presence of Inhibitors An inhibitor is a substance that prevents an enzyme from catalysing its reaction. It is an inorganic or organic compound that slows down or stops enzyme reaction Inhibitors: Reversible Inhibitors Competitive inhibitors Non-competitive inhibitors Irreversible inhibitors

Enzyme activity REVERSIBLE COMPETITIVE INHIBITORS. These competitors are not the substrate molecule and they thus compete with the substrate. If they are in high concentration they may essentially inactivate the enzyme. These are not damage the enzyme only form low-binding with the enzyme IRREVERSIBLE COMPETITIVE INHIBITORS. The competitor and substrate both compete for the active site but the competitor occupies the active site permanently thus deactivating the enzyme. Carbon monoxide is an irreversible competitive inhibitor of hemoglobin. Oxygen is the substrate. Penicillin is an irreversible competitive inhibitor. heavy metals, cyanide, nerve gas, and arsenic

Enzyme activity COMPETITIVE INHIBITORS are molecules that bind reversibly or irreversibly to the active site. Most naturally occuring competitive inhibitors are irreversible. it is a chemical that competes with the substrate molecule to bind the active site of the enzyme the inhibitor molecule is similar in structure to the substrate molecule.

succinic dehydrogenase is the enzyme Enzyme activity SUCCINIC ACID  FUMARIC ACID succinic dehydrogenase is the enzyme

Enzyme activity

Enzyme activity 2. NON-COMPETITIVE INHIBITORS have no structural similarity with the substrate, the inhibitor and substrate do not compete for space in the active site. the inhibitor reacts with some other part of the enzyme molecule. It may be reversible or irreversible. Reversible non-competitive inhibition is a major metabolic control mechanism

Enzyme activity 2. NON-COMPETITIVE INHIBITORS The inhibitor and the substrate do not compete for the same site. If the regulatory site is occupied by the inhibitor then the shape of the active site is changed so that the substrate molecules cannot fit and react. This type of inhibition, often called allosteric control

Enzyme activity

Enzyme activity

End Product Inhibition

Enzyme activity Feedback Inhibition

Sitation Longman A-level Course in Biology, Core Syllabus, Vol.1, Hoh Yin Kiong, pp. 87-103 Cambridge AS and A Level Biology, 2nd ed., Mary Jones & Friends, pp. 41-49 http://en.wikipedia.org/wiki/Enzyme http://www2.raritanval.edu/departments/Science/full-time/Weber/Microbiology%20Majors/Chpater5/chapter5sub/chapter5sub_print.html http://mandevillehigh.stpsb.org/teachersites/laura_decker/ap_enzyme_notes.htm