Understanding Enzyme Inhibition: Competitive, Uncompetitive, Non-Competitive, and Mixed Inhibition

max value the maximum rate of activity of that enzyme as well as the km value the michis constant is actually lowered

in uncompetitive inhibition now one major difference between uncompetitive and competitive is

the fact that in this particular case if we increase the substrate concentration that will not actually affect that

activity of the enzyme so uncompetitive inhibitors canot not be overcome by increasing the concentration of the

substrate and this is also true in a final type of inhibition known as non-competitive inhibition so we saw

that in competitive inhibition that inhibitor binds onto the active side of that enzyme because of the resemblance

in structure we saw that in uncompetitive the only time the inhibitor can bind onto that enzyme is

when the substrate is actually bound onto the active side of that enzyme because only then will we create that

pocket of space the alisic side that the inhibitor can actually bind to now we see that in non-competitive inhibition

sometimes the enzymes will have that active side as well as that additional pocket that additional alisic space

regardless of whether or not that enzyme is actually bound onto that substrate inside the active side so some enzymes

have a permanent alisic side that can bind Inhibitors and these Inhibitors are known as non-competitive Inhibitors

because they do not bind into the active side and so they do not actually compete for the active side with that substrate

and so these non-competitive Inhibitors can bind to the enzyme regardless of whether or not the substrate is actually

Bound in to the active side region and this is shown in the following diagram so we have the enzyme this is the active

side this is our alisic side to which the red um inhibitor can actually bind to so once we have this enzyme if we

have the substrate in close proximity and this is far away the substrate will bind onto the active side to basically

form this particular enzyme substrate mixture and then the enzyme substrate complex if no Inhibitors bound onto that

alisic side this can basically catalyze the transformation of that substrate the green molecule into the product and by

the way forgot to draw a product so let's say that that green structure is transformed into this final molecule

which is our product and this will only take place if no inhibitor is actually bound on to that alisic side now instead

we can also have this pathway that is followed if this is in close proximity it binds onto the alisic side to form

that enzyme inhibitor complex but just because we form the enzyme inhibitor complex that doesn't mean that the

substrate will not be able to bind into the active site in fact the substrate usually does spine into the active side

but the problem is once we form the enzyme substrate inhibitor as in this particular case that prevents that

enzyme from actually catalyzing the transformation of that green substrate into this purple product and so here no

reaction takes place now if the inhibitor departs then we form this enzyme substrate complex and only then

can it go on to form that particular product so unlike in competitive inhib inition and and unlike in uncompetitive

inhibition in non-competitive inhibition what The Binding of what The Binding of the inhibitor does is it lowers the

turnover number of that enzyme K cat so remember the kcat value the turnover number represents the number of

substrate molecules that can be transformed into the product n uh the product molecules over some period of

time by a single enzyme and what this inhibition does is it decreases that turnover number so essentially the VX is

lowered the turnover number is lowered but the km value the micha's constant value actually doesn't change in

non-competitive inhibition and again we'll talk about that in much more detail and why that actually takes place

in the next lecture so again reversible inhibition the inhibit binds onto that enzyme but it binds relatively weakly

and what that means is the dissociation can take place very quickly under the proper conditions and this is in

contrast to irreversible inhibition so in reversible inhibition we have three types we have competitive inhibition in

which that inhibitor binds directly to the active side we have uncompetitive inhibition in which the inhibitor binds

on to that alisic side that is formed only when that substrate is bound onto the active side of the enzyme and

finally we have non-competitive inhibition in which that enzyme always contains an alisic side and so what that

means is that inhibitor can bind onto that alisic side of the enzyme regardless of whether or not that

substrate is bound onto the active side of the enzyme and finally I guess I'll mention it briefly we also also have a

fourth type of inhibition known as mixed inhibition and in mixed inhibition what that inhibitor does is it basically

decreases the Affinity of that active side for that substrate and it also decreases the turnover number of that

particular enzyme this is known as mixed inhibition it's a much more complex type of inhibition than either of these three

forms of inhibition