HBG 3 ( Enzyme Characteristic and Regulation)

• Enzyme characteristics include the ability to increase the rate of reaction without changing the nature or being synthesized in laboratories, examples include metals and enzymes.
• All living things have enzymes, which are proteins except ribozymes, and can be denatured or degraded.
• Enzymes accelerate chemical reactions and are required for normal activity of cells in the body.
• Enzymes can be regulated and are often acting on one type of substrate.
• Enzyme kinetics involves the Michaelis-Menten rate equation.
• Enzyme regulation in the human body includes different types of enzyme regulation.
• Enzymatic activity deregulation leading to a metabolic disorder is an example of enzyme regulation.
• Catalysts increase the rate of reaction but do not change the nature or are synthesized in laboratories, examples include metals and enzymes.
• Enzymes are large molecules and can be denatured or degraded, accelerate chemical reactions, and are required for normal activity of cells in the body.
• Proteolytic cleavage is the irreversible removal of a portion of polypeptide chain by proteolytic enzyme.
• Pancreatic proteases are not synthesised in their final active form, they are synthesised in catalytically inactive molecules known as zymogens, which include trypsinogen, chymotrypsinogen, and procarboxypeptidase.
• Enzymes involved in the digestion of cellular debris and foreign materials are located within lysosomes.
• Different metabolic pathways occur in different cell compartments.
• Eukaryotic cells usually compartmentalize molecules such as enzymes into different organelles, a process known as enzyme regulation.
• Certain cellular processes are contained in separate organelles, for example, enzymes involved in the later stages of cellular respiration carry out reactions exclusively in the mitochondria.
• Zymogens must be cleaved to yield active enzymes.
• Enzymes are proteins except ribozymes, are large molecules and can be denatured or degraded, accelerate chemical reactions, and are required for normal activity of cells in the body.
• The basic enzymatic reaction can be represented as below : Substrate + Enzyme ⇌ Enzyme Substrate Complex (ES) ⇌ Product + Enzyme.
• The Michaelis - Menten equation is a model of enzyme kinetics which explains how the rate of an enzyme-catalysed reaction depends on the concentration of the enzyme and its substrate.
• The rate equation, also known as the velocity equation, is the equation in terms of substrate concentration.
• Km is the substrate concentration at which rate is 50 % of V max, also known as the measurement of the affinity an enzyme has for its substrate.
• Enzymes provide a transition state with a lower activation energy, allowing more substrate to reach the transition state (ES) and increase reaction rate.
• Km is also known as Michaelis constant.
• The rate expression is the equation in terms of velocity (v o) and substrate concentration [S].
• Km is the substrate concentration that gives V max / 2.
• Enzymes act as catalyst and increase the speed of chemical reaction without undergoing any permanent chemical change in themselves.
• If two enzymes, in different pathways, compete for the same substrate, then knowing the values of Km and Vmax for both enzymes permits prediction of the metabolic fate of the substrate and the relative amount that will flow through each pathway under various conditions.
• Common modifications include the addition of phosphate, methyl, acetyl groups.
• Covalent modification represents the first step of a multistep sequence and can control the whole sequence effectively.
• Examples of enzymes regulated by covalent modification include many enzymes and non-protein helpers such as Iron (Fe 2 +), Magnesium (Mg 2 +), Coenzymes, and Cofactors.
• Allosteric Regulation of Threonine Deaminase in bacteria involves binding of small molecules to the allosteric site, leading to a change in the enzyme conformation (active site).
• Many enzymes are also regulated by covalent modification, which involves the addition or removal of specific chemical groups to activate or inactivate the enzyme.
• Mode of regulation of metabolic pathways such as glycolysis (glucose to pyruvate) involves P sending back a signal to slow the line to inhibit enzyme 1.
• Some modifications can be reversed.
• Process of negative feedback control involves an increase in P leading to a decrease in its rate of production by inhibiting Enzyme 1 at the site topographically distinct from the site of active site (allosteric site).
• Allosteric inhibitory site mutation can lead to increased PRPP levels, which in turn leads to increased purines and hyperuricemia.
• Defect in Allosteric Regulation can lead to conditions such as Gout, where Phosphoribosylpyrophosphate (PRPP) is high in Red Blood Cells (RBC) of patients with gout.
• Metabolic pathways (MP) involve many enzymes and regulation of only a small number of enzymes involved in control of homeostasis is insufficient.
• Aldehyde dehydrogenase (ALDH) is an enzyme that catalyzes the conversion of acetaldehyde to acetate.
• pH changes can also influence enzyme activity.