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Chem- Enzymes

Chemistry SCC 10/2011

enzyme a protein molecule that catalyzes chemical reactions without itself being destroyed or altered
catalyst a substance that increases the rate of a chemical reaction but is not consumed or changed by it.
substrate a substance upon which the enzyme acts
denaturation the partial or total alteration of the structure of a protein without change in covalent structure by the action of certain physical procedures or chemical agents. Any disruption of the protein structure that is accompanied by a loss of activity
cofactor nonprotein molecules that must bind to a particular enzyme before a reaction occurs (natural reactant – usually a metal ion or a coenzyme)
coenzyme a diffusible, heat-stable substance of low molecular weight that when combined with an inactive protein called an apoenzyme forms an active compound or a complete enzyme called a holoenzyme
apoenzyme the protein part of an enzyme
prostheticgroup the coenzyme bound tightly to the enzyme
holoenzyme the functional compound formed by the combination of an apoenzyme and its appropriate coenzyme
zymogen Some enzymes, mostly digestive enzymes, are originally secreted from the organ of production in a structurally inactive form
activation energy the energy required for a molecule to form an activated complex; in an enzyme-catalyzed reaction, corresponds to the formation of the activated enzyme substrate complex
enzyme-substrate complex (E-S) a molecule of substrate is bound to the active center of the enzyme molecule
active site where the initial binding of substrate and enzyme occurs
absolute specificity meaning that the enzyme combines with only one substrate and catalyzes only the one corresponding reaction
group specificity they combine with all substrates containing a particular chemical group
first-order kinetic reaction a reaction in which the rate of reaction is proportional to the concentration of substrate
zero-order kinetic reaction a reaction in which the rate is independent of the concentration of substrate, and depends on enzyme concentration only
activator Inorganic cofactors, such as chloride or magnesium ions; They increase the catalytic activity of an enzyme when it binds to a specific site
inhibitor interfere with the reaction, decrease the rate of reaction; can be either reversible or irreversible
uncompetitive inhibitor binds to the enzyme-substrate complex so that increasing substrate concentration results in more ES complexes to which the inhibitor binds and thereby increases the inhibition so there is no product.
competitive inhibitor binds to the active site of an enzyme and competes with substrate for the active site
noncompetitive inhibitor binds an enzyme at a place other than the active site so no competition between inhibitor and substrate, examples are heavy-metal ions such as lead and mercury
Fixed time reaction the amount of change produced by the enzyme is measured after the reaction is stopped (usually by inactivating the enzyme with a weak acid) at the end of a fixed time interval and a measurement is made of the amount of reaction that has occurred
continuous monitoring method the reaction is monitored continuously, usually of absorbance change every 30 or 60 seconds. Continuous measurements are preferred because any deviation from linearity is readily observable
isoenzyme one of a group of related enzymes catalyzine the same reaction but having different molecular structure and characterized by varying physical, biochemical, and immunological properties; subunit of the enzyme
NAD nicotinamide adenine dinucleotide, example of a coenzyme
NADP nicotinamide adenine dinucleotide phosphate, example of a coenzyme
Two-substrate reaction more than one substrate yields more than one product and the concentrations of both substrates affect the rate of reaction
six classes of enzymes : a. Oxidoreductases b. Transferases c. Hydrolases d. Lyases e. Isomerases
What are enzymes composed of Proteins
What factors influence the actions of enzymes - Substrate concentration - Enzyme concentration - Temperature - pH - activators - inhibitors
What unit of measurement (activity) is used to express enzyme concentration International Unit -(U/L) Katal (mol/s) -Katals per liter (Kat/L).
How does temperature affect enzyme-catalyzed reactions? At what temperature are MOST enzyme catalyzed reactions performed? optimal is 37°C; rate of an enzymatic reaction is proportional to its reaction temperature, until the temperature is high enough to denature the protein composition of the enzyme
At what pH are MOST enzymes optimally active? Optimum pH is where the reaction rate is the fastest, must look at the pH activation curve for each enzymes optimum pH.
What enzymes and isoenzymes do we associate with the heart and MI's (myocardial infarction)? CK, CK isoenzymes, LDH, LDH isoenzymes, AST, Troponin-I
What enzymes and isoenzymes do we associate with the liver and hepatic disease AST, ALT, GGT, ALP, LDH (LDH-5), and 5’-NT
What enzyme and isoenzyme is associated with bone disorders? ALP, ALP isoenzymes, ACP
Which enzymes are associated with pancreatic disease AMS, LPS
Which enzyme is associated with prostate disease ACP
Which enzymes and isoenzymes are associated with muscle disorders CK, CK-MM, AWST, LDH (LD4 & LD5)
List the isoenzymes of CK and identify the tissue location of each. CK-BB – brain CK-MM – skeletal muscle CK-MB – cardiac muscle (used in diagnosis of MI)
List the isoenzymes of LD/LDH and identify the tissue source of each. LD-1 & LD-2 – cardiac muscle and RBCs LD-3 – lungs and spleen LD-4 & LD-5 – liver and skeletal muscle
What is the effect of hemolysis on MOST enzyme reaction tests Falsely elevated results
What is the specimen of choice for most enzyme tests Serum
Created by: CZUPAN



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