Biochemistry Enzymes VI: Regulatory Enzymes

Hello and welcome back to Educator.com, and welcome back to Biochemistry.0000

Today, our topic is going to be regulatory enzymes; regulatory enzymes do exactly what the name suggest.0004

They regulate the speed of certain processes.0011

Most enzymes participate in metabolic pathways.0016

The product of one enzyme reaction becomes the substrate for the next enzyme reaction and on down the line.0020

One or more of those enzymes in a metabolic pathway is going to regulate the flow of substrates through there.0027

It controls what the body needs when it needs it - very, very important regulatory enzyme activity.0034

OK, let’s see what we have got.0040

Let’s repeat what we just said in writing here.0044

In metabolism, both catabolic and anabolic groups of enzymes, they work in sequences - excuse me - called metabolic pathways to achieve a certain goal, and that goal is some molecule that they need to either completely breakdown or completely synthesize.0048

OK, now, the product of one enzyme in the sequence - excuse me - as we said, becomes the substrate for the next enzyme in the sequence.0097

OK, a good example of this is glycolysis.0137

It is going to be one of the first metabolic pathways that we actually look at when we get to the second part of this class.0141

An example - oops - is glycolysis, and glycolysis is the breakdown of the conversion – I will go ahead and call it the breakdown because it is a catabolic pathway - the breakdown of 1 glucose molecule to 2 molecules of something called pyruvate, 2 molecules of pyruvate.0149

It is a beginning of how the body metabolizes the sugar that you intake in order to produce energy.0191

OK, the sequence goes like this.0199

We have glucose going to glucose 6-phosphate going to fructose 6-phosphate going to fructose 1,6-biphosphate going to glyceraldehyde-3-phosphate and dihydroxyacetone.0203

The dihydroxyacetone is converted to another molecule of glyceraldehyde-3-phosphate.0228

Now, we have 2 glyceraldehyde-3-phosphates.0236

This goes to 1,3-biphosphoglycerate, goes to 3-phosphoglycerate, goes to 2-phosphoglycerate, goes to phosphoenolpyruvate, and then, finally, we have our pyruvate.0242

This is a metabolic pathway; it is glycolysis.0264

These are the individual steps, and each step is catalyzed by a particular enzyme- a separate enzyme.0266

OK, we have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10 enzymes in this metabolic pathway.0277

One or more of these enzymes is going to be a regulatory enzyme.0284

It is going to control the flow of glucose through this pathway.0288

I mean, this is the first one; this is the last one.0294

Now, the regulatory enzyme does not have to be the first or the last.0298

It tends to be often, and it can be somewhere in the middle, too; but ultimately, what it is controlling, it is controlling the flow of the initial substrate all the way through product.0302

That is all that is going on here; OK, let’s see.0312

One or more enzymes along a given pathway, they have the capacity to affect the overall rate of the pathway.0317

I will just say the rate at which substrate flows through the pathway - it is probably a little better description - by increasing or decreasing catalytic activity.0352

As you can see, the reason the body works as well as it does is because of this regulation.0386

There are millions of things going on, millions of reactions happening simultaneously.0394

The body needs to maintain a certain steady state, some reasonable degree of equilibrium at all times, but the body is subject to all kinds of external effectors, if you will- temperature, hydrogen ion concentration, the food that we eat, all kinds of things going on, immune stress.0398

The body needs to adjust that- regulatory enzymes, regulatory proteins.0420

That is what they do - OK - in catalytic activity - alright - in response to specific signals, obviously, in response to specific signals.0425

For example, if there is too much of certain molecule in the body and the body needs to, sort of, cut that back so that excess is actually used up, a regulatory enzyme will shut down a particular pathway that is producing that molecule temporarily until that concentration of molecule diminishes, and then it will open up the flood gates again to allow more- that is it.0444

That is all that is going on here- specific signals.0464

OK, those are the regulatory enzymes.0468

Now, these - let me go back to black, I like black, actually, oh, 2, oh, nice - regulatory enzymes do exactly what they are named for.0470

They regulate the overall rate at which substrate and/or product appears or disappears- very, very intuitive notion.0517

There is nothing particularly counterintuitive about regulation; we do it all the time in our daily lives.0540

OK, now, let’s talk about some of the mechanisms of regulation, what do enzymes do to regulate, how do they go about it.0544

OK, let me go to...I have some green ink now- very nice.0551

I will go to blue; OK, the first one we are going to talk about is called allosteric regulatory, an allosteric mechanism, allosteric regulatory enzyme.0560

OK, this is one that requires the reversible - very, very important - binding of a second substrate - actually, I do not want to call it a substrate, I was going to put it in quotes, but I will not do that - the binding of a second molecule at an allosteric site.0582

An allosteric site just means, it is another site on the enzyme.0624

That is not the active site of the enzyme; that is all it means, just a fancy name for another site somewhere else on the enzyme, so it could be...if the substrate binds here, well, the allosteric site might be close by.0629

It might be over here; it might belong to a completely different subunit.0640

If you have a multi-subunit protein, which is often the case, allosteric sites are often found on other subunits of the protein.0643

A regulatory enzyme is one that requires the reversible binding of a second molecule at an allosteric site - OK - not the active site.0651

OK, now, these second molecules are called...we want fancy names for them.0668

They are called allosteric modulators, and again, modulation is just a fancy word for change.0685

They are allosteric changers, allosteric modulators or allosteric effectors.0690

You are going to see all of these words floating around in the literature.0695

Now, they can be metabolites; they can be anything.0702

They can be metabolites; they can be intermediates along the pathway, not necessarily initial product - I am sorry - not necessarily substrate or final product.0707

They could be anyone in the metabolites in between, or they can be metabolites that have molecules that have nothing to do with the actual pathway itself.0719

They can come from completely different source; it can be anything.0729

Just think of it as a random molecule; they can be metabolites.0735

They can be cofactors; you know, we have talked about cofactors.0738

They can be small molecules; they can be the actual substrate itself.0744

It can also act as an allosteric modulator, so the substrate can actually control how that enzyme does what it does; so I will just put etc.0751

OK, that is one process; we are going to be looking at this in detail in just a minute, but I just want to list the process.0765

Allosteric regulation usually involves some other site on the protein.0771

It could be a single subunit protein; it could be a multi-subunit protein.0777

It is just another site that affects how the enzyme does what it does.0781

OK, another process is something called covalent modification, so another way that modification.0787

OK, covalent modification - let me see if I am actually going to be defining it a little bit later - activity is modulated by adding or subtracting.0807

OK, covalent modification, this is the covalent.0813

I am going to talk about this a little bit later, but I might as well go ahead and write it down now.0819

It is the covalent - now, I will write it this way - adding or subtracting some molecular group covalently.0824

Let's say you have a particular enzyme that is doing something.0850

If we add some small molecule to it, let say, a phosphoryl group , a PO₃^2- and attach it covalently somewhere on the protein, now, because that protein has that thing attached to it, it is either going to be more active or less active depending on the nature of the particular enzyme.0855

That is what we mean by covalent modification; we do something to the protein, add or subtract some molecular group.0875

It could be anything; it could be a big group.0880

It could be a small group, and it changes the nature.0881

It changes the catalytic activity of that enzyme, and it is done covalently.0885

OK, now, in either case, in the case of covalent modification or allosteric regulation, the regulatory enzymes, they tend to be multi-subunit proteins.0895

Multi-subunit because it allows for, well, a greater degree of complexity just by nature of the fact that you have multiple subunits, and we already know that proteins, they, sort of, they shift.0929

They move; they breathe, if you will.0942

A change in one part of a protein in a different subunit has a greater degree of control on the shift that takes place near the active site.0945

Regulatory proteins, because of their complex nature, they tend to be multi-subunit because it allows for a greater control, and that is really what we want.0955

The body wants really, really fine-tuned control.0964

It does not want broad strokes control; it wants very, very fine strokes control- detailed, very, very careful.0970

OK, we have allosteric regulation, and we have covalent modification.0977

I am going to list 2 other mechanisms, and we may talk about them a little bit towards the end.0982

There are 2 other regulatory processes.0991

One is addition or interaction of a regulatory protein.1002

OK, let's make sure that we have everything straight here because we already know that enzymes are proteins.1013

We are using the word protein and enzyme; let’s see if we can straighten this out.1024

You have an enzyme; it needs to be regulated in some capacity.1029

Well, one of the ways that that happens is, you have other proteins that interact with the enzyme in regulatory capacity.1033

In other words, their job is to interact with the enzyme in order to help regulate the enzyme.1042

Those are the regulatory proteins, so we definitely differentiate.1047

In this particular case, the regulatory enzyme itself, we specifically refer to it as an enzyme unless we are talking about it generically as a protein.1054

When we say regulatory protein, we are not talking about the regulatory enzyme itself.1061

We are talking about the protein that interacts with it in order to help regulate the enzyme- very, very important.1066

OK, and another process that occurs is proteolytic cleavage- very fancy name for basically just cutting off a piece of the protein, of the enzyme, to make it active as opposed to its, sort of, being inactive.1073

Proteolytic cleavage is where the enzyme activates or regulates when peptide fragments are removed from the enzyme.1096

Now, it is important to know about proteolytic cleavage, is that proteolytic cleavage is irreversible.1134

Once you cut off a piece of that enzyme to activate it or let it perform its regulatory function, it is not going to go back.1140

Now, if the body needs it, it is going to have to produce a new version of that enzyme.1149

Proteolytic cleavage is irreversible.1155

The other processes, they are reversible.1159