Lecture 9: Inhibition Flashcards
What are the 2 different ways of inhibitors can bind, and what do the 3 classes of inhibition discussed fall into
Reversible : non covalent, rapid dissociation of the EI
(un,non, competitive)
Non reversible: covalent modification of an enzyme
What is the essential principle behind how inhibitors work on enzymes
Inhibitors are able to bind to the enzyme making an EI complex that means that that enzyme can’t make product.
Are inhibitors chemically altered by the enzyme when it binds to stop enzyme reactions
no
What is competitive inhibition, how it reduces rate of catalysis and its effect on the Km and Vmax,
Competitive inhibition is where inhibitors (chemically similar to substrate) compete with substrate for the active site of an enzyme, therefore reducing the rate of catalysis by reducing the proportion of enzyme molecules bound to a substrate.
It can be overcome by adding excess substrate, so the Vmax is the same, but the Km increases because the more substrate is needed to attain the same rate.
What is non-competitve inhibition how it reduces rate of catalysis and its effect on the Km and Vmax,
Non-competitive inhibition is where inhibitors bind to the enzyme at a distant site from active site which is not dependent on the formation of ES complex. This decreases the conc of functional enzyme rather than decreasing ES vs EI therefore resulting solution behaves like dilute solution- decreased turnover number (reduce kcat).
The Km value is the same but the Vmax has decreased.
What is un-competitve inhibition how it reduces rate of catalysis and its effect on the Km and Vmax,
Uncompetitive inhibition is where the inhibitor can only bind to a site on the enzyme after substrate has bound. ESI complex is unproductive so there will always be some ESI complex present if there is I, and Vmax will be lower in the presence of inhibitor. Km gets smaller as [I] increases
Which inhibition types aren’t helped by increasing substrate conc
Uncompetitive and non competitive
What is on the x and y axis for the lineweaver burk plot for inhibitors, vs their normal graph
ON the lineweaver burk, y : 1/v whereas normal its v. On lineweaver burk the x is 1/ [S] but on normal its [S]; they are reciprocals
How can Ki be found from a secondary plot for a competitive vs a non competitive inhibitor
The secondary plot of a competitive is made using slopes (at different concentrations/different trials) whereas for non competitive it is the y intercepts. The -Ki is found from the x intercept of the secondary plot.
What is the Ki and what size is Ki when binding is strong
The affinity that the inhibitor binds to an enzyme, ===dissociation constant capital Kd such that a small Ki means that inhibitor is bound more tightly
Which type of mimetic inhibitor binds more strongly : substrate or transition state
Transition state by 10^3 smaller
How do you calculate the new Km app for competitive inhibition. And how has this Km changed?
KMapp= Km x (1 + [Inhibitor] / [Ki]).
Kmapp has increased
How do you calculate the new Vmax app for noncompetitive and uncompetitive inhibition. And how has this V max changed?
Vmax app = V max / (1 + [Inhibitor] / [Ki])
Vmax has decreased
How do you calculate the new Km app for uncompetitive inhibition. And how has this Km changed?
KMapp = Km / (1 + [Inhibitor] / [Ki])
Kmapp has decreased
How do you tell competitive, non competitive and uncompetitive apart
competitive is competing with the substrate because they are chemically similar. Non competitive is not a competitor in that it has separate relations with the enzyme at a distant binding site.
Uncompetitive doesn’t want to fight against the substrate because the substrate helps it to bind.
