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Enzyme
BIOCHEMISTRY (CHM3)
Our Lady of Fatima University
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WEEK 7 - BIOCHEM MIDTERM
LECTURE #1 ENZYMOLOGY
Enzymes – a specific (mostly, protein but some are ribonucleic acids) biocatalyst that is essential in physiologic functions such as nerve conduction, muscle contraction, degradation of nutrients, and energy usage. All cells in the body have thousands of different enzymes. Inactive forms of enzymes called zymogens (proenzymes) are larger in structure and must be hydrolyzed to be activated**.** May exist in different forms or isoforms called isozymes and allozymes based in their physical properties such as electrophoretic mobility, solubility, or resistance to inactivation. May be specific biomarker for disease in specific tissues. “Isozymes represent enzymes from different genes: Allozymes represent enzymes from different alleles of the same gene. Can be used interchangeably.”
ENZYME STRUCTURE Active site - a water-free cavity the binding site of a substrate. Allosteric site – binding site of regulator molecules. 2 CLASSIFICATION OF ENZYMES 1. Simple enzyme – an enzyme composed only of protein. 2. Conjugated enzyme - enzyme composed of protein and non-protein part.
Enzyme additional components (accessories) include: Cofactor – “helper molecules” that regulate catalytic reactions. Activator – inorganic cofactors usually a metallic ion (Zn2+, Mg2+, Mn2+, Fe2+) and non-metallic ion (Cl-) necessary for enzyme activity. Coenzyme - organic cofactors such as vitamins.
Enzyme - Cofactor = Apoenzyme (inactive) Enzyme + Cofactor = Holoenzyme (active)
2 TYPES OF COENZYMES
- Prosthetic group – permanently bound to an enzyme.
- Co-substrate – transiently bound to an enzyme.
COFACTORS 1. Activators Common metallic activators include; Calcium, Iron (II), Magnesium (II), Manganese (II), Zinc and Potassium. Common non-metallic activators; Bromine and Chloride Modulates enzymatic reactions 2. Coenzymes Organic cofactors that are usually nucleotide phosphates and vitamins. When coenzymes are bound to enzymes, the coenzyme portion is now called a prosthetic group. Increases enzymatic reactions.
ENZYME PROPERTIES Catalysis - ability to accelerate the rate of a chemical reaction. Enzyme Specificity – the capacity of a protein catalyst to bind to a selected molecules/substrates. Enzymes are stereoselective - asymmetric active site. Has two known models for binding specificity; 1. The lock and key model – the shape of the binding site is the same shape of the substrate. No shape change. 2. The induced fit model – the shape of the binding site is flexible and adapts to shape of the substrate. The enzyme changes shape. Enzyme Concentration and Activity – concentration of enzymes is directly proportional to the rate of synthesis and degradation. Molecular Basis for Enzyme Catalysis – concentration of substrates is directly proportional to the rate of synthesis.
ENZYME NOMENCLATURE
Commonly name for its function rather than its structure. Substrate – substances that enzymes catalyzes. Product – resulting substance after catalysis. The use of suffixes “- ase” and “- in” (old nomenclature) denotes the substance as an enzyme. Prefixes such as “oxid-“ (redox reaction) and “hydrol-“ (hydrolysis) refers to an enzyme types of reaction they catalyze. The identity of the substance is often noted in addition to the type of reaction such as glucose oxidase, pyruvate carboxylase and succinate dehydrogenase.
ENZYME CLASSIFICATION Enzymes are classified based on their functional properties. The class of the enzymes is also the basis of the Enzyme Commission (EC) code of the International Union of Biochemistry and Molecular Biology (IUBMB) which contains 4
digits separated by decimal points. The 1st digit dictates the enzymes classification. Enzymes classes includes;
- Oxidoreductases – catalyzes the redox (oxidation-reduction) reaction between two substrates.
- Transferases - catalyzes the transfer of a non- hydrogen bound group of a substrate to another substrate.
- Hydrolases – catalyzes the cleavage of covalent bonds with the use of water.
- Lyases - catalyzes the removal of groups from substrate without the use of water; usually yields double bonds to products.
- Isomerases - catalyzes the isomerization of molecules.
- Ligases - catalyzes the formation of bonds coupled with the hydrolysis of ATP.
ENZYME KINETICS First-order Kinetics Reaction rate ~ concentration of substrate. Occurs when enzyme concentration [E] outweighs substrate concentration [S]. Zero-order Kinetics Vmax of reaction rate ~ [E] Occurs when substrate concentration [S] outweighs the enzyme concentration [E].
**MEANS OF MEASURING ENSYME ACTIVITY
- Michaelis-Menten Curve**
Km = Michaelis-Menten constant
Enzyme
Course: BIOCHEMISTRY (CHM3)
University: Our Lady of Fatima University
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