Understanding Enzymes Flashcards
What is the meaning of Km?
this is the dissociation constant - substrate concentration where 50% of Vmax is reached
What is the meaning of Km?
this is the dissociation constant - substrate concentration where 50% of Vmax is reached
is a measure of affinity
What is the meaning of Kcat?
Turnover of enzyme: substrate complexes.
A constant which measures the enzyme dissociation of the EP, it is called the turnover number and is related to V/Max
How is the enzymatic reaction enhances by cofactors?
Cofactors increase the affinity for the enzyme (lowering of Km)
They can increase the Vmax hence increase Kcat
How is this relevant in haemostasis? For the prothrombinase complex? What are the roles of FV, FX and phospholipid?
Xa and IIa naturally have a high Km and a low Vmax
FactorVa increases the Vmax, it orientates the the substrate for faster cleavage
The phospholipid provides a surface for the reaction to occur on and this reduces the Km by bringing Xa and IIa together to increase affinity.
Accumulates to 10^6 increase in Kcat/Km
What happens with an increase of the enzyme concentration?
You get an increase in the vmax
What is the effect of a decresed Km?
It means increased affinity for enzyme
Kcat/Km?
the specificity constant and is an absolute measure of catalytic efficiency
What is the role of enzymes in the the protein C activation?
Thrombomodulin increases Vmax
Phospholipids again provide the surface for activation - reduced Km
Summarise Kcat and Km
Things which change the active site increase Kcat, things that increase the chance of binding by physically bringing them closer decrease the Km
What is the role of the fibrin clots?
Provides the surface for the activation of plasminogen to plasmin by increasing Vmax and decreasing Km
