control 1

I want to talk now

shift gears from talking about

noncompetitive and competitive

inhibition. And remember,

we're not talking about uncompetitive

inhibition here. You probably do in

bio chem class. But I want to talk about

allosteric control. An allosteric

control can be either inhibition

or activation. Allosteric literally

means other site. In this case, you have two different

binding sites on the surface

of an enzyme. But almost always

the enzyme is a multi subunit en, often one of the

sub units is the business end that has the catalytic

site or sites. And then another sub unit, or type of sub unit has

the regulatory sites. If you think about

allosteric enzymes, they're either going to

bind an inhibitor and an activator at the

allosteric site. What happens is

that that changes the confirmation of

the overall protein. By, by changing the confirmation

that will either activate the enzyme

and facilitate the reaction or

inhibit the reaction. I like this diagram

a lot out of an intra textbook

just because good visual what you

see here as you see an allosteric enzyme on the left that is

being inhibited. And you'll notice

that what happens is when the

inhibitor binds to a regulatory subunit and a regulatory

allosteric site that changes the

conformation of the active sites such that no product is formed. On the other hand, in the absence

of the inhibitor that enzymes in a

high affinity form for the substrate

and product is made in the case of

allosteric activation. Here you see a

similar thing, where the allosteric

regulator binds to a

regulatory site. But here it stabilizes the enzyme in a form that is much better able to bind to substrate and facilitate the reaction. Here, you're

actually stabilizing the form of the enzyme

that is active. Most allosteric

enzymes have both an inactive form

and an active form, and it's all dependent

on who's bound, and that's going to vary from enzyme to enzyme. Allosteric enzymes have more than two sub units. Here's an enzyme, it doesn't really

matter what it is. It's part of

pyrimidine synthesis. What you see here are

multiple sub units, in blue and green

and in yellow. And the yellow

sub units happen to have regulatory sites, in this case, inhibition sites where CTP binds. And if you're making these nucleotide triphosphates, the one of the products is CTP that's going

to inhibit this enzyme that's

very early on in that metabolic pathway to make these pyrimidines. Ctp is going to bind to these regulatory or allosteric

inhibition sites on multiple sub units,

and in doing that, it shifts the entire

conformation of those blue and those

green sub units such that the substrate can't get in and bind

well to the active site that's in a pocket between those flu and those

green sub units. Here, this allosteric

regulation is basically switching this enzyme off into an inactive form. That's going to be very common in what we call

feedback control, where the final product

of a pathway will allosterically

regulate one of the early enzymes

in a pathway. What you'll see

in terms of allosteric

regulation a lot is that the allosteric

activator inhibitor will change the

conformation of the pool of enzymes that

are available and whether or not

they're active. Here we have a situation where there's an enzyme. It reacts with

glucose, with sugars. But if there's no ADP, those enzymes are

inactive. Think about it. Guess a pathway that this enzyme might be

involved in. Let's just think it takes glucose and it's going to do something

else with it. But it's only

active when there's a DP bound to it. When do you have

a lot of ADP? You have lots of ADP when you've

used up a lot of your ATP here. The ATP ADP is a

signal for low energy. Only when there's

a high amount of ADP relative to

the amount of ATP, it will bind to the

allosteric cytes. In this case,

it stabilizes the conformation of the enzyme in such

a way that now it's actually going to facilitate the reaction. Now, those enzymes

will react with the glucose and

bind the glucose. You see this idea of

allosteric enzymes being having both an active form and

an inactive form. And depending on

the regulator, those regulatory

molecules will bind to the allosteric

cytes and either turn on or turn

off the enzyme, make the conformation the active conformation, or make it the

inactive conformation.I want to talk now