Enzymes

Enzymes

When many people hear the word enzyme, they immediately think of the word catalyst.  I think of cupid who facilitates 2 people falling in love by shooting one of them in the butt with an arrow.  Regardless of where the arrow hits, cupid is increasing the rate at which 2 people fall in love.  Enzymes increase the rate of reactions.  I have a few common enzymesProteins that speed up chemical reactions in the body. here that you might be familiar with:  Natures Miracle commonly has enzymes in it that breakdown urea and other products that come in urineThe liquid waste excreted by the kidneys..  It smells like a vets office; I’m sure my cats hate me using it.  I also use Rid-Ex because I live in the middle of nowhere and have a septic system.  And here we have a bottle of the lactase enzyme which catalyzes the breakdown of lactoseA disaccharide sugar found in milk. into glucoseA simple sugar that is the main source of energy for cells. and another monosaccharide named galactose.  I have a picture of a rotting hamburger here next to a non rancid hamburger to remind you that these reactions would occur naturally, just over a long period of time.  If you were to ingest this hamburger exposing it to your digestive enzymes, the breakdown of said hamburger would happen much more quickly than if you were to leave it on the counter top to just rot.  Actually, there’s fungus in every environment.  Overtime the hamburger will inevitably get colonized by fungus which will expose the hamburger and the bread to fungal digestive enzymes and break it down at a rate at which it can support the life of the fungus.

Activation energy

To understand how enzymes participate in reactions, we should review some terms first.  I know this example is silly but I’m a visual learner, and this is a great visual for understanding how reactions proceed.  In both situations here we’re going to start with the reactants or the raw materials which are these dry frogs.  As our reaction proceeds each frog will jump over into the waterThe universal solvent essential for life. becoming a product or what is produced which, in this case, is a wet frog.   Think of the word product; it’s what’s produced.  In math you have 2 * 2 equals 4 and 4 is the product.  In order to get our dry frogs to become wet frogs there is a barrier to this reaction.  That barrier is called the activation energyThe minimum amount of energy required to start a chemical reaction..  Activation energyThe capacity to do work or cause change. is what is needed to be overcome in order to get the reaction started.  In our picture, the activation energy is the pile of rocks. The frogs have to jump over this pile of rocks in order to get the reaction started.  This is very important: enzymes do not contribute activation energy.  They lower the activation energy that’s required to start the reaction and therefore they lower the barrier to the reaction.  Think about all the different ways you can start a fire.  Some are really easy like a lighter and some are a little bit more difficult like rubbing 2 sticks together.  Your method is the barrier to the reaction and the better your method is the quicker you are going to start your fire.

Enzyme anatomy

Because enzymes are proteinsLarge molecules made of amino acids with various functions in the body., they have very specific shapes.  One area on an enzyme is called the active siteThe specific region of an enzyme where a substrate binds and a reaction occurs..  This is the place where a substance known as a substrate can bind to the enzyme.  Of course, the active site has a shape that specifically fits the shape of the substrate, like a lock and key.  Because enzymes are proteins and have again that specific shape, they are not multitaskers.  This means that the enzyme lactase will work only with lactose as its substrate; the enzyme sucrase will work only with sucrose as its substrate; and the enzyme urease will work only with urea as its substrate.  As you can see -ase is a common ending among enzymes.  When enzyme and substrate bind they are believed to have an induced fit resulting from the very specific shapes.  This specificity means that if you lose your lactase enzyme, no one else will step up and do the job.  Bummer.

Catalytic cycle

The catalytic cycle is a reaction of catabolismThe metabolic process that breaks down molecules to release energy. or breakdown using an enzyme.  Here our substrate is sucrose, our enzyme is surcease, and our final product will be the monosaccharides glucose and fructose.  Note how water is required for this reaction.  Therefore this reaction is known as hydrolysis or hydro lysis.  Hydro meaning water and lysis meaning to split.  You can see how sucrose binds to the enzyme’s active site.  The bond between the 2 monosaccharide is broken, and the products are released from the enzyme.  This is very important to realize: The enzyme is not used up and is available for another reaction with another molecule of sucrose. 

Denaturing enzymes

The word denatureThe process in which a protein loses its shape and function due to heat or pH changes. means to lose shape.  Chemicals like strong acids and bases can denature enzymes.  Heat is another denaturing agent.  If you denature an enzyme, the active site will change shape and the substrate will no longer be able to fit.  Therefore, the enzyme will not be able to participate in accelerating the reaction rate.  I have some examples here of ways to denature proteins or denature enzymes.  The proteins in this egg have been denatured with heat which is why the texture changes during cooking.  These other examples are all examples of how acids can denature enzymes in the same way that heat can.  Many people use acidicA solution with a pH below 7, having a higher concentration of H⁺ ions. substances on meat like steak sauces.  Your muscle proteins can be denatured by lactic acidA substance that releases hydrogen ions (H⁺) in solution. as well as milk proteins that contribute to the characteristic texture of yogurt.  Fish can be cooked sous vide and is considered fully cooked when exposed to acidic substances like citrus juices.  In the same way, a good sour mix is made with an egg that is denatured or cooked buy lemon juice before water and sugar is added. 

Enzyme Inhibitors 

There are other ways to stop enzymes from working aside from denaturing it.  A competitive inhibitor is a molecule that will sit in the active site and prevent the substrate from binding. This is like someone sitting in your seat. A non competitive inhibitor has a docking site away from the active site.  When docked a non competitive inhibitor can do many things to prevent the substrate from binding.  A common hormone in the body named angiotensin 2 is the culprit of high blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. for many Americans.  People with high blood pressure are sometimes put on drugs called ACE inhibitors such as captopril, shown here.  ACE is the angiotensin converting enzyme that produces Angiotension II and by blocking this enzyme, Angiotensin II is not made, and its effects that produce high blood pressure are prevented.