Enzyme Substrate Complex

When you hear the word enzyme, you probably think of Proteins. If so, you'd be correct, as Enzymes are a type of protein. Proteins are famously known to be in many foods, including eggs, dairy, fish, and meat. All over the media, influencers recommend different protein shakes to supplement our diets. But did you know that proteins can also be naturally found within our bodies? Enzymes are natural proteins found in our bodies that are similar to race car accelerators, as they are famously known to speed things up, but they can also form complexes. To learn more about enzymes and the enzyme-substrate complex, keep reading!

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Table of contents

    Enzyme substrate complex overview

    The enzyme-substrate complex is a molecule that is made up of many different parts. This complex forms when an enzyme gets into "perfect contact" with its respective substrate, sometimes causing a change in the shape of the enzyme.

    When the substrate comes into a space called the active site, weak bonds are formed with the substrate. If a conformational or shape change occurs in the enzyme, it sometimes makes two substrates combine or even split molecules into smaller components.

    The enzyme-substrate complex is essential to our bodies because our bodies' metabolic processes need to occur fast enough to keep our systems functioning and alive.

    Metabolic processes are all the combined vital chemical reactions that occur in living organisms that are required for survival.

    An example of a metabolic process is cellular Respiration, which is the process in which glucose is broken down and converted to chemical energy, or ATP.

    ATP, or adenosine phosphate, is an energy-carrying molecule that provides Cells with a usable form of energy.

    Some essential things to understand regarding the enzyme-substrate complex are:

    • The enzyme-substrate complex is temporary.
    • After the enzyme-substrate complex changes, it creates a product that can no longer bind to the enzyme.
    • After the product is released from the enzyme-substrate complex, the enzyme is now free to bind to another substrate.
    • This means we only need a few Enzymes in our Cells as they can be continually used.
    • We can think of enzymes as machines whose function is to speed up biochemical reactions occurring in our bodies. They do this by lowering the activation energy needed to kickstart the reaction.

    This section serves as an overview of the enzyme-substrate complex. In the following few paragraphs, we will discuss some of these concepts and definitions in more detail.

    Enzyme substrate complex definition

    The enzyme-substrate complex is a temporary molecule that occurs when an enzyme binds perfectly with a substrate.

    Enzymes are Proteins referred to as biological catalysts that speed up chemical processes in living organisms. Enzymes usually end with the suffix "-ase" because the first recognized enzyme was diastase, which catalyzes the breakdown of starch into maltose sugars.

    Some important definitions to know regarding the enzyme-substrate complexes are:

    Proteins are organic compounds with many valuable and vital roles within our bodies.

    Other vital roles of proteins include:

    • building and repairing the tissues in our bodies
    • defending our Immune System by making Antibodies
    • providing energy when carbohydrate and lipid levels are low in our bodies
    • Muscle Contraction with proteins like actin and myosin
    • keeping the shape of our cells and bodies (ex) collagen in our skin

    For more regarding proteins, please refer to our articles "Proteins," "Structural Proteins," or "Carrier Proteins."

    Enzymes work by lowering the activation energy of chemical reactions. In biology, the activation energy can be considered the minimum energy required to activate molecules so that the reaction can begin or occur.

    Enzymes lower activation energies by binding to substrates in a way where the chemical bonds break and form more easily.

    Substrates are the molecules that enzymes bond within active sites to form an enzyme-substrate complex. Depending on the type of reaction, we can have more than one substrate. For instance, in specific reactions, the substrates can be broken down into many products, or two substrates can even combine to make one product.

    Active sites are the areas within the enzymes that the substrate binds or where the action occurs.

    Enzymes are proteins, which means they are made up of amino acids. Amino acids have different side chains or R groups that give them their unique chemical properties. This creates a unique environment for each enzyme-substrate complex at the active site. This also means that the enzymes bind to specific substrates, making them known for their specificity.

    Enzyme substrate complex formation

    As previously mentioned, the enzyme-substrate complex formation happens when an enzyme and substrate combine. We can compare the enzyme and substrate interaction as jigsaw puzzle pieces fit together.

    When we talk about the enzyme-substrate complex model, we can speak of two "fits."

    • Lock and Key model:
      • This model occurs when the enzyme's active site fits like a lock to the substrate, which works like a key.
      • Think of opening the door together into your house. In this case, your house key is the substrate, and the door's lock represents the enzyme. If the substrate or house key fits perfectly, then the door opens, or in the case of the enzyme, it can activate and function.
    • Induced Fit model:
      • This model occurs when the substrate binds, causing a change in shape in the enzyme's active site, and can be referred to as the hand-in-glove model.
      • This is because the first finger is usually hard to insert into a glove, but once we do and the glove has adequately aligned, then it's easy to put on the glove. We will expand on this in the section "Enzyme substrate complex diagram."
    The Enzyme Substrate Complex Lock and Key Model Study Smarter Figure 1: Lock and Key model. Wikibooks, Waikwanlai (Public Domain).

    Enzyme substrate complex diagram

    The induced fit model is more widely accepted for the enzyme-substrate complex. This type of enzyme-substrate complex diagram is considered better because scientists believe it can better explain how catalysis happens. This is because the induced fit model introduces a more dynamic interaction between enzyme and substrate than the Lock and Model figure does.

    Catalysis occurs when a catalyst or enzyme speeds up a reaction.

    The Enzyme Substrate Complex Induced Model Study SmarterFigure 2: The induced fit model diagram. Wikimedia, TimVickers (Public Domain).

    1. The substrate enters the active site of the enzyme.
    2. The enzyme/substrate complex is created. Since this is the induced model we are referring to, the enzyme changes shape slightly as the substrate binds. Depending on the chemical reaction and properties of the amino acids, some reactions might occur better in an environment with water, without, acidic, etc.
    3. Then, the products are created and released by the enzyme.
    4. After the product's release, the enzyme changes to its original shape allowing it to be ready for the next substrate.

    Enzyme substrate complex example

    Enzymes can be regulated where their activity can be reduced or enhanced by different kinds of molecules.

    • Competitive inhibition occurs when a molecule competes with the substrate for the enzyme's active site directly by binding to it and preventing the substrate from doing so.

    • Noncompetitive inhibition occurs when a molecule binds to a site other than the active site, which we call the allosteric site. However, this molecule still prevents the substrate from binding to the enzyme's active site.

    A noncompetitive inhibitor usually does this by causing a conformational or shape change at the enzyme's active site as it binds to an allosteric site. This change in shape inhibits or doesn't allow the substrate to attach to the enzyme's active site anymore. This type of molecule could also be referred to as an allosteric inhibitor.

    Differences between when the enzyme-substrate complex regularly reacts (a) and is inhibited by a noncompetitive inhibitor (b).

    • Most allosterically regulated enzymes have more than one protein subunit.

    A protein subunit is a single molecule made of proteins that combines with other single protein molecules to make a protein complex.

    This signifies that when allosteric inhibitors bind to one protein subunit at an allosteric site, all the other active sites on the protein subunits change shape slightly so that the substrates bind less efficiently. Less efficiency means that the rate of reaction is lowered.

    • Allosteric activators also exist, and they work the same as inhibitors, except they increase the affinity of the enzyme's active sites for its substrates.

    The Enzyme Substrate Complex Reaction vs Inhibition Study SmarterFigure 3: Enzyme reaction and inhibition. Wikimedia, Srhat (Public Domain).

    Enzyme-substrate complexes generally have three parts: enzymes, substrate, and product. Depending on the reaction being performed, there can be more than one substrate or product.

    Featured below are some common enzyme-substrate complex examples.

    Enzyme Substrate(s)Product(s)
    Lactase Lactose Glucose and galactose
    MaltaseMaltose Glucose (two)
    Sucrase Sucrose Glucose and fructose

    The substrates and products shown in the table are carbohydrates. Carbohydrates are organic compounds that are used to store energy in our bodies.

    To help you better understand what's happening in the table featured above, we will go over how the lactase enzyme-substrate complex works.

    The lactase enzyme substrate:

    • The lactase enzyme breaks down lactose, our substrate, into glucose and galactose products. Breaking down lactose is crucial because it helps us digest dairy products. When humans don't make enough lactase enzymes, they are lactose intolerant and have trouble digesting dairy products. Lactose is also called milk sugar.

    Honorary enzymes- a participation trophy?

    Hemoglobin is a protein inside our red blood cells (RBCs) that carries oxygen throughout our bodies.

    You can think of it as a car with four seats or active sites; the passengers are essentially oxygen. Oxygen is transported throughout our bodies by hemoglobin to keep us alive.

    Hemoglobin is considered an allosteric protein because hemoglobin consists of four protein subunits. Also, oxygen binding at the active sites is affected by inhibiting molecules binding to an allosteric site. For example, carbon monoxide can bind to hemoglobin lowering its efficiency to bind with oxygen resulting in carbon monoxide poisoning.

    They are honorary proteins because, even though they have allosteric and active sites, they do not have catalytic activity!

    Enzyme Substrate Complex - Key takeaways

    • The enzyme-substrate complex forms when an enzyme gets into "perfect contact" with its respective substrate, sometimes causing a change in shape in the enzyme.
    • The enzyme-substrate complex is essential to our bodies because our bodies' metabolic processes need to occur fast enough to keep our systems functioning and alive.
    • When we talk about the enzyme-substrate complex model, we can speak of two "fits." The Lock and Key model and the Induced Fit model.

    • Enzymes are proteins referred to as biological catalysts that speed up chemical processes in living organisms.

    • An example of an enzyme-substrate complex involves maltose. The enzyme is maltase, the substrate is maltose, and the product is two glucose.

    References

    1. ScienceDirect, Enzyme Substrate Complex, Medical Biochemistry, 2017.
    2. Mary Ann Clark, Matthew Douglas, Jung Choi, Biology 2e, 28 Mar 2018.
    Frequently Asked Questions about Enzyme Substrate Complex

    What does the enzyme-substrate complex produce? 

    The enzyme-substrate complex is a temporary molecule that occurs when an enzyme binds perfectly with a substrate. It lowers the activation energy of critical metabolic reactions, often producing broken-down products of substrates that are important for our bodies to function, such as glucose.

    What is an enzyme-substrate complex?

    The enzyme-substrate complex is a temporary molecule that occurs when an enzyme binds perfectly with a substrate.

    What are the 3 parts of an enzyme-substrate complex?

    Enzyme-substrate complexes generally have three parts: enzymes, substrate, and product. 

    How is an enzyme-substrate complex formed?

    The enzyme-substrate complex formation happens when an enzyme and substrate combine forming weak bonds.

    Why are enzyme-substrate complexes important?

    The enzyme-substrate complex is essential to our bodies because our bodies' metabolic processes need to occur fast enough to keep our systems functioning and alive. 

    Test your knowledge with multiple choice flashcards

    What are honorary enzymes?

    What are the parts of the enzyme-substrate complex?

    What is the enzyme of the lactase-lactose complex?

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