EXAM (enzymes)

• Practical/Trivial Name


  According to the name of the substrate with the addition of the suffix “ase”
• Practical/Trivial Name


  • Lipase- enzymes acting on lipids
  • Protease- enzymes acting on proteins
• Enzyme Nomenclature

  Enzymes can be named practically/trivially or systematically
• The first number in the systematic name defines the class to which the enzyme belongs, while the next two numbers indicate subclass and subclass to which the enzyme is assigned. The last number is a specific serial number to each enzyme in its subclass
• Enzymes


  Biologic proteins that catalyze biochemical reactions without altering the equilibrium point of the reaction or being consumed or changed in composition
• Systematic Name


  According to the numerical designation given by the Enzyme Commission (E.C.)
• General Classification of Enzymes

  • Oxidoreductases
  • Transferase
  • Hydrolase
  • Lyases
  • Isomerases
  • Ligases (Synthetases)
• Transferase

  Catalyze the transfer of a chemical group from one substrate to another
• Systematic Name

  • Lactate dehydrogenase- E. C. 1. 1. 1. 7
  • Amylase- E. C. 3. 2. 1 .1
  • Alanine aminotransferase- E. C. 2. 6.1. 2
• Oxidoreductases


  Involve removal or addition of electrons (reduction-oxidation ["redox"] reaction) and involve oxygen molecule
• Hydrolase

  • Esterases, Acid phosphatase (ACP), Alkaline phosphatase (ALP), Cholinesterase (CLS), Lipase (LPS), Peptidases, Trypsin (PTS), Pepsin (PPS), Leucine aminopeptidase (LAP), Glycosidase, Amylate, Amylo 1,6 glycosidase, Galactoxsdases
• Hydrolase


  Hydrolyze the splitting of a bond by the addition of water (hydrolysis reaction)
• Lyases


  Remove groups from substrate without hydrolysis, leaving only double bonds in the molecular structure of the product
• Isomerases


  Catalyze the intramolecular rearrangement of the substrate compound
• Transferase

  • Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Creatine kinase (CK) or creatine phosphokinase (CPK), Gamma glutamyl transferase (GGT), Ornithine carbamyl transferase (OCT)
• Oxidoreductases

  • Oxidase, Cytochrome oxidase, Dehydrogenase, Lactate dehydrogenase (LDH), Malate dehydrogenase (MDH), Isocitrate dehydrogenase (ICD)
• Lyases

  • Aldolases, Glutamate decarboxylase, Pyruvate decarboxylase, Tryptophan decarboxylase
• Isomerases

  • Glucose phosphate isomerase, Ribose phosphate isomerase
• Terms associated with enzymes: Holoenzyme - an active substance formed by the combination of a coenzyme (cofactor- need another activator to form reaction) and apoenzyme. Apoenzyme - the protein portion subject to denaturation, in which the enzyme loses its activity. Catalytically inactive protein when cofactor is removed. They are heat labile and dialyzable. Isoenzyme - enzymes present in an individual with similar enzymatic activity but differ in their physical biochemical and immunologic characteristics
• Ligases (Synthetases)

  Synthesis - joins two substrate molecules together using the energy released from hydrolyzing a pyrophosphate bond to a high-energy phosphate compound
• Metalloenzyme


  Enzyme whose metal ions are intrinsically part of the molecule
• Coenzyme


  Organic molecule that hastens enzymatic reaction but undergoes a change or is consumed to another product
• Coenzymes

  • NAD – Nicotinamide Adenine Dinucleotide
  • NADP - Nicotinamide Adenine Dinucleotide Phosphate
• Proenzyme


  Inactive precursor of enzymes, also referred to as zymogens
• Enzyme Kinetics


  An enzyme catalyses a reaction by combining with its substrate to create an enzyme-substrate complex. The complex can dissociate back to E + S or breakdown to product and free enzyme
• Michaelis-Menten Constant: V = Vmax(S) / Km + (S)
• The Michaelis-Menten equation accurately describes virtually all single-substrate enzyme-catalyzed reactions and many bisubstrate reactions
• Koshland's Induced Fit Theory


  Based on the attachment of a substrate to the active site of an enzyme, causing conformational changes in the enzyme
• Emil Fisher's Lock and Key Theory


  Based on the rigid enzyme molecule into which the substrate fits like a key into a lock
• The Michaelis-Menten equation gives the means to determine total enzyme concentration in serum and other body fluids
• Metal ion activators

  • Amylase - needs Cl, Br-
  • LDH - needs Zn2
  • Lipase - needs Ca++
• Temperature

  The rate of any chemical reaction is usually increased 2-3 times for every 10 degrees Celsius rise in temperature
• Zero Order Reaction - the rate of reaction is linear with time, independent of the concentration of substrate and directly proportional to enzyme concentration
• Substrate concentration

  An increase in substrate concentration produces an increase in the rate of reaction, reaching a maximal value at a particular concentration of substrate. Higher concentrations do not result in increased rate of reaction (Saturation kinetics)
• KOSHLAND’S INDUCED FIT THEORY is based on the attachment of a substrate to the active site of an enzyme, which then causes conformational changes in the enzyme. This theory is more acceptable because the protein molecule is flexible enough to allow conformational changes and also allow some explanation on the influence of hormones on enzymatic activity
• Factors Affecting Enzyme Reactions
• First Order Reaction - the rate of reaction is determined by the concentration of substrate. The rate of reaction changes continuously with time as the substrate is consumed, increasing the rate
• Hydrogen Ion Concentration or pH


  Enzymatic reactions proceed at their fastest rate at an optimum pH and are considerably slowed or stopped at higher or lower pH values
• Types of Reaction Order

  • Zero Order Reaction
  • First Order Reaction
• Non-competitive Inhibitor - substances do not resemble the substrate and bind to the enzyme in areas other than the active site