Structural & Molecular Basis of Drug Action (L4,5) Flashcards
What is an isozyme?
Different enzymes that catalyze the same reaction
What are the 3 classifications of cofactors?
1) Bound METALS
2) Loosely bound organic molecules (COENZYMES)
3) Tightly bound organic molecules (PROSTHETIC GROUPS)
Hydrogen bonding in active site of GLUCOKINASE favors binding ____ over ____.
Glucose over galactose
What kind of protease is chymotrypsin?
It is a Serine Protease
(b/c it has a Ser 195)
What is the Michaelis-Menton Equation for Simple enzyme kinetics?
Vi= (Vmax[S])/(Km+[S])
Name 3 irreversible inhibitors (that do so through covalent modifications)
1) DFP (covalent modification of acetylcholinesterase)
2) Penicillin (mimics D-Ala-D-Ala that allows it to bind to and modify transpeptidase enzymes that cross link bacterial walls)
3) Aspirin (binds to Cyclooxygenase I and II via a two-step kinetic scheme)
What are suicide inhibitors?
Give an example of one and how it works!
They are substrate analogs that bind to active sites and are converted to an active form.
Allopurinol (used to treat gout) binds to xanthine oxidase and is converted to oxypurinol, which binds with extremely high affinity to the enzyme that produces urate preventing the enzyme from producing urate
What is the difference b/w Reversible competitive inhibitors and reversible NONcompetitive inhibitors?
Reversible competitive inhibitors: bind to ACTIVE site and compete with the substate
Reversible NONcompetitive inhibitors: bind to ALTERNATE site and change the conformation of the enzyme
What variables change and don’t change with reversible COMPETITIVE inhibitors?
Vmax WONT change
Km WILL change
What variables change and don’t change with reversible NONCOMPETITIVE inhibitors?
Km WONT change
Vmax WILL change
What are allosteric enzymes?
Multisubunit enzymes with MULTIPLE active sites
NOTE: This means non Michaelis-Menten kinetics
What are homo/heterotropic effectors?
Homotropic effector: the substrate itself binds to one active site and affects other active sites
Heterotropic effector: A substance that is NOT the substate and does NOT bind to the active site
Allosteric enzymes exist in LOW and HIGH affinity states, which are referred to as ____ and ____ forms, respectively.
Tense (T); Relaxed (R)
Homotropic effectors often result in _____ cooperativity.
In this regard, how do they change the properties of substrate binding to other active sites?
What type of graphical curve does this produce?
What is the hill coefficient?
Positive cooperativity;
Binding of substrate to one active site INCREASES AFFINITY (Km) of substrate binding to other active sites.
An enzyme exhibiting positive cooperativity produces a SIGMOIDAL curve.
Hill coefficient (n) is a measure of the degree of cooperativity
What is feedback inhibition and what type of allosteric regualtion is this?
It is when the products of an enzyme rxn act as allosteric inhibitors.
This is an example of HETEROTROPIC ALLOSTERIC effector
Covalent modifications like phosphorylation occurs on ____.
What 2 enzymes are required for this?
AA’s that have hydroxyl (-OH) groups
eg Ser, Thr, Tyr.
1) Kinase ADDS phosphate grp
2) Phosphatase REMOVES phosphate grp
What does a protein ending in “-ogen” mean?
It is describing an enzyme in the inactive form!
What is the slope, y intercept, and x intercept equations for the lineweaver-burk plot?
slope=Km/Vmax
Y intercept=1/Vmax
x intercept= –1/Km
How can you estimate Km experimentally?
It is the concentration of the substrate at which Vi is 1/2 of Vmax
Serine proteases are a class of enzyme in general _____.
Acid/base catalysis
Where will the serine protease chymotrypsin cleave peptides?
Chymotrypsin is cleaved by what enzyme?
At the CARBOXYL side of Tyr, Trp, and Phe.
Trypsin, which has an ACID pocket that binds BASIC residues
