Each year over 500 tons of protease enzymes are added to laundry detergents to break down proteins such as the pizza stains on your shirt. These enzymes are produced by bacteria grown in huge stainless steel tanks.

ENZYMES

1. What are enzymes?- Biological molecules that catalyze, or speed up, chemical

reactions in biological systems by lowering their activation energy

- Activation Energy Initiates Reactions : In any chemical reaction, an initial stable state must become less stable before change is possible

WHY ENZYMES?• Energy is required to begin any reaction (activation

energy)• If the activation energy is large the reaction will proceed,

but too slowly for biological systems

• Cells manufacture specific proteins to speed up reactions without being used up– Ex. In red blood cells carbonic anhydrase enables

carbon dioxide and water to form 600 000 molecules of carbonic acid per second (in test tube: about 200 per hour)

2. How enzymes work- Enzymes Lower the Energy Barrier

- Although the activation energy is lower in an enzyme-catalyzed reaction than in an uncatalyzed reaction, the energy released is the same with or without catalysis. In other words, Ea is lower, but ΔG is unchanged.

- An enzyme is a protein catalyst with an active site capable of binding one or more substrate molecules, forcing them into the transition state

• Enzymes have several ways of causing their substrates to enter the transition state:

(A)orientation,- Bring substrates in the correct position

(B) physical strain- Make bonds weaker and easier to rearrange

(C) chemical charge- add/remove ions to destabilize the substrate

(D) Induced fit-Some Enzymes Change Shape When Substrate Binds to Them -- Shape changes result in an induced fit between enzyme and substrate, improving the catalytic ability of the enzyme

3. Catalyzed Reactions Reach a Maximum Rate - Because there is usually less enzyme than substrate present, the reaction rate levels off when the enzyme becomes saturated.

4. Enzyme Activity is regulated

a) Enzymes can be activated my co-enzymes/ co-factors

b)Enzymes can be inhibited, by inhibitors - Inhibitors can be reversible/irreversible- Inhibitors can be competitive (bind to active site) or

noncompetitive (allosteric)

Ex. Irreversible Inhibition DIPF forms a stable covalent bond with the side chain of the amino acid serine at the active site of the enzyme trypsin, thus irreversibly disabling the enzyme.

Reversible Inhibition: A competitive inhibitor binds temporarily to the active site of an enzyme

A noncompetitive inhibitor: binds temporarily to the enzyme at a site away from the active site. In both instances, the enzyme’s function is disabled for only as long as the inhibitor remains bound.

• Sensitivity to alcohol• [Notes/Highlighting]• [Resource Table of Contents]• A Catalyst for Alcohol The enzyme aldehyde dehydrogenase catalyzes an important step in the breakdown of alcohol.• The guests were at their tables as the bride and groom entered the room to enthusiastic applause. Champagne glasses were raised in the first of many

toasts. But no sooner had Frank drunk his first small glass of bubbly than he started feeling ill. With his face flushed and his heart beating rapidly, he excused himself and left the reception. It was hours before he felt normal again. The same thing had happened to him before, also when he drank a small amount of an alcoholic beverage.

• There are people who can drink a lot of alcohol without getting sick, and there are others, like Frank, who become ill after consuming only a small amount. These individual differences are a function of the biochemistry of alcohol once it enters the body. Typically, a series of two chemical reactions transforms ethyl alcohol (the alcohol in beverages) into acetate in the body: first ethyl alcohol is transformed into acetaldehyde, then acetaldehyde is transformed into acetate.

• These reactions constitute a metabolic pathway, in which the product of the first reaction, acetaldehyde, serves as the raw material for the second. Neither reaction can occur to any appreciable extent without help. Each reaction needs to be “speeded up” by a different catalyst—a specific enzyme.

• A Precursor to Trouble Some people have a weakly active form of the aldehyde dehydrogenase enzyme. When they drink alcohol, acetaldehyde accumulates in their bodies, with ill effects.

• Enzymes are proteins, and as such, each has a specific amino acid sequence. The enzyme that speeds up the second reaction in the metabolism of alcohol is aldehyde dehydrogenase (ALDH), which has 517 amino acids. Most of the guests at Frank’s table had the same amino acid sequence in their ALDH. In this “typical” sequence, the 487th amino acid is glutamic acid, whose side chain carries a negative charge (see Table 3.1). The other guests' ALDH folded into the correct three-dimensional structure, and the enzyme did its job—speeding up the conversion of acetaldehyde into acetate. In Frank’s cells, however, the amino acid at position 487 is lysine instead of glutamic acid; lysine has a positive charge. This seemingly tiny difference is enough to change the three-dimensional structure of ALDH and interfere with its catalytic function.

• Because of its structural defect, Frank’s ALDH works, but only slowly. When he drank that small glass of champagne, the first metabolic reaction (the conversion of alcohol to acetaldehyde) happened quickly, but the second reaction (the conversion of acetaldehyde to acetate) did not. And, whereas alcohol has some pleasant effects on the body, the effects produced by acetaldehyde are not so pleasant. As acetaldehyde accumulated in his body, Frank became ill. His facial flushing and accelerated heartbeat were typical short-term effects of acetaldehyde; in the longer term, it can cause brain abnormalities and even some cancers.

• Frank’s atypical ALDH sequence shows how individual differences in alcohol tolerance are not necessarily behavioral, but can be due to differences in basic biochemistry. (So think twice before kidding a person because he or she can't “hold his liquor.”)

Allostery and Reaction Rate How the rate of an enzyme-catalyzed reaction changes with increasing substrate concentration depends on whether the enzyme is allosterically regulated.

Feedback Inhibition of Metabolic Pathways The commitment step is catalyzed by an allosteric enzyme that can be inhibited by the end product of the pathway. The specific pathway shown here is the synthesis of isoleucine, an amino acid, from threonine in bacteria. This pathway is typical of many enzyme-catalyzed biological reactions.

5. Enzyme activity is influenced by surrrounding conditions

a) pH Affects Enzyme Activity - Each enzyme catalyzes its reaction at a maximum rate at a

particular pH. Ex. pepsin is a protease active in the acidic environment of the stomach.

b) Temperature Affects Enzyme Activity - Each enzyme is most active at a particular optimal temperature. At higher temperatures, denaturation reduces the enzyme’s activity.