Catalytic Strategies Flashcards
What is the dissociation constant equivalent to?
Kd is equivalent to the ligand (hormone) concentration at which half of the receptors are occupied.
Give an example of three serine proteases (endopeptidases).
Chymotrypsin, Trypsin and Thrombin.
What is the primary specificity of Chymotrypsin and Tryspin?
Chymotrypsin cleaves C-terminally or aromatic residues (Phe, Trp and Tyr).
Trypsin cleaves C-terminally of basic residues (Arg and Lys)
What amino acids are found in the “catalytic triad” (active site) of serine proteases?
Serine, Histidine and Aspartate.
What is the function of the “oxyanion hole” in serine proteases?
It functions to stabilise the negative charge on the tetrahedral intermediate.
Give two characteristics of “Coagulation Factors”
1) They are all serine proteases.
2) They all have the same “primary specificity” as trypsin.
Which coagulation factors are Vitamin-K dependent?
Factor VII, IX, X and II (prothrombin)
What is the role of Vitamin K in blood coagulation?
Its acts as a cofactor for gamma-carboxylase, which functions to post-transitionally modify the glutamate residues in coagulation factors to form gamma-carboxyglumatic acid.
What is the role of gamma-carboxyglutamate (Gla) coagulation?
Gla increases the coagulation factors’ binding affinity for calcium ions. This in turn helps to mediate the binding of the coagulation factors to their substrates and cofactors.
What complex catalyses the conversion of prothrombin to thrombin?
The Prothrombinase Complex.
What constitutes The Prothrombin Complex?
Factor Xa, Ca2+, Factor Va and phospholipids.
Why is Vitamin-K recycling useful?
Vitamin K recycling lowers the requirement for vitamin K from dietary sources and bacteria.
What enzyme helps to recycle vitamin?
Vitamin K Epoxide reductase.
Name two ways Vitamin K deficiency can arise?
1) When the body cannot properly absorb the vitamin K made by the bacteria in the gastrointesntial tract.
2) After long-term treatment with antibiotics.
How does Warfarin act as an anticoagulant?
It acts as a coagulant by by blocking the action of Vitamin K epoxide reductase, preventing vitamin K recycling.
As a result, gamma-carboxylation of coagulation factors is inhibited, which will affect their functioning.
