Enzymes In Medicine Flashcards
What are the assumptions of the Michaelis-Menten model?
(1) After a certain time the breakdown and formation of the ES are the same (enzyme-substrate complex) (Steady State)
(2) Measuring initial rates of reactions (before appreciable formation of product)
(3) The reaction goes forward but does not go backwards
What is the Michaelis constant (Km)?
Km is the combination of the rate constants for the formation and disappearance of ES (enzyme-substrate complex)
Km = (k2+k3)/k1
Velocity of formation of ES = k1[S][E]
Velocity of breakdown of ES = (k2+ k3)/[ES]
What is the Michaelis-Menten equation?
Velocity = (Vmax [S])/ (Km + [S])
What does the graph of velocity (V) vs. substrate concentration [S] look like for enzymes that behave according to Michaelis-Menten kinetics?
Note: The Michaelis constant Km is the substrate concentration [S] yielding a velocity V = Vmax / 2.
What is the equation for the Lineweaver-Burk plot?
(1/V) = [(Km/Vmax)(1/[S])] + (1/Vmax)
What are irreversible enzymes?
Irreversible enzymes are inhibitors that form a stable covalent bond with the enzyme resulting in permanent inactivation of the enzyme. Irreversible enzymes remove the enzyme from the reaction and cause a decrease in Vmax but no change to the value of Km. Irreversible enzymes can bind to the active site of enzymes and compete for substrate.
What are reversible inhibitors?
Reversible inhibitors bind enzymes with noncovalent interactions and dissociate rapidly from the enzyme to allow the enzymes to recover their original activity.
What is a competitive inhibitor?
Competitive inhibitors bind to the enzyme and compete with the substrate for the enzyme’s binding site.
What is a noncompetitive inhibitor?
A noncompetitive inhibitor binds the enzyme at a site other than the active site, which causes a change in the enzyme structure so that it does not work as efficiently. Noncompetitive inhibitors do not usually resemble the substrate. Note: a noncompetitive inhibitor can bind to both the enzyme E and the enzyme substrate complex ES.
What is an uncompetitive inhibitor?
An uncompetitive inhibitor binds to the enzyme substrate complex (ES). As the inhibitor binds and stabilizes the ES complex, it makes it more difficult for the substrate S to dissociate or be converted to product, increasing enzyme affinity for S and so reducing substrate Km.
What is a coenzyme?
A coenzyme is a nonprotein small molecule that is necessary for the functioning of an enzyme and is often derived from vitamins. Deficiencies in coenzymes can cause disease (e.g., Vitamin C deficiency can cause scurvy).
What is a co-substrate?
A co-substrate is a nonprotein molecule that is necessary for the function of an enzyme and is often modified during a catalytic reaction (e.g., ATP).
What is a cofactor?
A cofactor is a small, nonprotein molecule that binds to many enzymes and facilitates catalytic activity. An enzyme with its cofactor is active and called a holoenzyme, and an enzyme without its cofactor is inactive and called an apoenzyme. Some enzymes use metal ions as cofactors (e.g., Zn2+, Mg2+, Mn2+, Ni2+)
What are the four categories of enzyme regulation?
The four categories of enzyme regulation are allosteric regulation, covalent modification (e.g., phosphorylation and dephosphorylation), enzyme level modifcation (e.g., transcription and translation), and compartmentation/compartmentalization (localization of enzymes to specific organelles in the cell).
What is allosteric regulation?
Allosteric regulation is a specific category of enzyme regulation. Allosteric enzymes do not behave according to M-M kinetics, but rather exhibit a sigmoidal activity relationship between velocity and substrate. Allosteric regulation occurs by an effector molecule (activator or inhibitor) binding to a regulatory site (a site other than the active site).
