Question | Answer |
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 |