Enzymes Flashcards
Serum ; Reagent
Enzyme concentration ; Substrate concentration
↑ Enzyme concentration =
Enzyme > substrate, substrate =
↑ reaction rate
↑ reaction rate
When substrate concentration reaches a maximal value, higher concentration of substrate no longer results in increased rate of reaction
Saturation kinetics
Nonprotein entities
Cofactors
Organic compound (Ex. NADP)
Coenzymes
↑Coenzyme =
↑ Velocity
Inorganic ions
Activators
Alters spatial configuration of the enzyme for proper substrate binding
Activators
Ex. Ca2+ (#1 activator), Zn2+ (LDH), Cl- (AMS), Mg2+ (CK, ALP)
Activators
Inorganic ion attached to a molecule
Metalloenzymes
Ex. Catalase, cytochrome oxidase
Metalloenzymes
Interferes with the enzymatic reactions
Inhibitors
Binds to the active site of an enzyme
Competitive inhibitor
Reversible (Substrate > Inhibitor)
Competitive inhibitor
Binds to the allosteric site (cofactor site)
Noncompetitive inhibitor
Irreversible
Noncompetitive inhibitor
Binds to the enzyme-substrate complex
Uncompetitive inhibitor
↑ Substrate =
↑ ES = ↑ Inhibition
Same catalytic reactions but slightly different molecular structures ; Fractionation
Isoenzymes
Ex. NADP
Coenzymes
= optimum temperature for enzyme activity
37’C
↑ Temperature =
↑ Reaction rate (↑ movement of molecules)
Denaturation of enzymes
40-50’C
Inactivation of enzymes
60-65’C
For every 10OC increase in temperature, there will be a two-fold increase in enzyme activity
Temperature coefficient (Q10)
Most physiologic reactions occur in the pH range of
7-8
Storage
Enzymes: = for longer period of time
Substrate and Coenzymes:
LDH (LD4 & 5):
-20’C
2-8’C
Room temperature
Mostly increases enzyme concentration
Hemolysis
Decreases enzyme concentration
Lactescence or milky specimen
Enzyme nomenclature
1st digit:
2nd and 3rd digits:
4th digit(s):
classification
subclass
serial number
Enzyme classification
“OTHLIL”
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
Redox reaction
Oxidoreductases
Dehydrogenases
-Cytochrome oxidase
-LDH
-MDH
-Isocitrate dehydrogenase
-G-6-PD
Transfer of a chemical group other than hydrogen from 1 substrate to another
Transferases
Kinases, Transaminases, Aminotransferases:
-CK
-GGT
-AST
-ALT
-OCT
Hydrolysis/splitting by addition of water
Hydrolases
Esterases
-ACP
-ALP
-CHS
-LPS
Peptidases
-Trypsin
-Pepsin
-LAP
Glycosidases
-AMS
-Galactosidases
Removal of groups w/o hydrolysis (product contains double bonds)
Lyases
Decarboxylases
-Glutamate decarboxylase
-Pyruvate decarboxylase
-Tryptophan decarboxylase
Intramolecular arrangements
Isomerases
Glucose phosphate isomerase
Isomerases
Ribose phosphate isomerase
Isomerases
Joining of 2 substrate molecules
Ligases
Synthases
Ligases
Water-free cavity
Active site
Where the substrate interacts
Active site
Cavity other than the active site
Allosteric site
May bind regulatory molecules
Allosteric site
Coenzyme that is bound tightly to the enzyme
Prosthetic group
Apoenzyme + Prosthetic group
Holoenzyme
Inactive form of enzyme
Zymogen/proenzyme
Shape of the key (substrate) must fit into the lock (enzyme)
Emil Fisher’s/Lock and Key theory
Based on the substrate binding to the active site of the enzyme
Kochland’s/Induced fit theory
Acceptable theory
Kochland’s/Induced fit theory
Enzymes catalyze reactions by lowering the activation energy level that the substrate must reach for the reaction to occur
Enzyme kinetics
Enzyme combines w/ only 1 substrate and catalyzes only 1 reaction
Absolute specificity
Enzymes combine w/ all the substrates in a chemical group
Group specificity
Enzymes reacting w/ specific chemical bonds
Bond specificity
Reaction rate depends only on enzyme concentration Independent on substrate concentration
Zero-order reaction
Reaction rate is directly proportional to substrate concentration
First-order reaction
Independent on enzyme concentration
First-order reaction
Measurement of enzyme activity
Change in substrate concentration
Change in product concentration
Change in coenzyme concentration
1 micromole of substrate/minute
International Unit
Unit 1 mole of substrate/second
Katal
Absorbance is made at 10-second intervals for 100 seconds
Nonkinetic assay
pH = 10.5 ; 405nm
Alkaline Phosphatase