Enzymes 2 Flashcards
What reaction do glucokinase and hexokinase catalyse?
conversion of glucose to glucose-6-phosphate
What properties do glucokinase have? (Km and Vmax)
high Km and High Vmax
Where do you find glucokinase activity?
the liver
What are isoenzymes?
enzymes that catalyse the same reaction
What technique is a useful way to separate plasma proteins?
electrophoresis
In reference to the action of enzymes with 2 or more substrates, what is meant by an ordered sequential mechanism?
pyruvate to lactate by enzyme lactate dehydrogenase is an example of this mechanism
- the enzyme exists in a ternary complex first with the substrates of the reaction and then after with the products of the reaction
so in this example,coenzyme NADH always binds first and lactate is always released first
What is a random sequential mechanism?
the order of binding and release of substrate and product is random but a ternary complex still forms first with substrates and then the products of the reaction
What is a double displacement or ‘ping-pong’ reaction?
example is transamination process
no ternary complex formed
What are allosteric enzymes?
enzymes that change their conformation on the binding of an effector which in turn causes an apparent change in binding affinity at a different ligand binding site
haemoglobin is an example of this
What is an uncompetitive enzyme inhibitor?
one that binds to the enzyme at an area other than the active site
What is a competitive inhibitor?
one that binds to the active site, preventing the normal substrate from binding
What does a competitive inhibitor do?
will compete with substrate molecule for active site
What does the presence of a competitive inhibitor do to the Km and Vmax values?
Km increases - decrease in affinity of enzyme for substrate
Vmax remains unchanged
Why does the Vmax not change in the presence of a competitive inhibitor?
increasing the substrate concentration can overcome the inhibition
What is a ‘real world’ example of a competitive inhibitor?
the drug AZT working to inhibit the reverse transcriptase used by HIV to produce the dsDNA
What is an example of a drug that works on the transition state rather than the substrate?
oseltamavir
What does a non-competitive inhibitor do?
bind to enzymes non covalently and will usually attach to a site other than the active site of the enzyme
What effect does a non-competitive inhibitor have on the Km and Vmax?
Km remains unchanged
Vmax will decrease
Why does the Km remain unchanged in the presence of a non-competitive inhibitor?
the substrate is usually still able to bind to the active site
How does an irreversible inhibitor bind to the enzyme?
covalently
What are the 2 ways regulatory enzymes modulate reactions?
- allosteric enzymes
- covalently modified enzymes
What is meant by feedback inhibition in reference to regulating enzymes?
example would be build up of product inhibiting enzyme by binding to a part other than the active site resulting in a conformational change
What are allosteric effectors?
usually cell metabolites and will either increase or decrease the efficiency of substrate binding
are examples of non-competitive inhibitors
How can enzymes be regulated by covalent modification?
example is by phosphorylation
