8/10/2019 ERT211 Chp 1-2.pdf

1/27

ERT 211/1

Biochemical Engineering

CHAPTER 1:THE KINETICS OF ENZYME

CATALYZED REACTIONS

BY:

EN. MOHD. FAHRURRAZI TOMPANG

8/10/2019 ERT211 Chp 1-2.pdf

2/27

Classification of Enzyme

Enzymes fall into 6 classes based on function

1. Oxidoreductases: which are involved in oxidation,reduction, and electron or proton transfer reactions

2. Transferases : catalysing reactions in which groupsare transferred

3. Hydrolases : which cleave various covalent bonds byhydrolysis

4. Lyases : catalyse reactions forming or breakingdouble bonds

5. Isomerases : catalyse isomerisation reactions

6. Ligases : join substituents together covalently.

8/10/2019 ERT211 Chp 1-2.pdf

3/27

8/10/2019 ERT211 Chp 1-2.pdf

4/27

Enzyme Reaction

For design and analysis of a reacting system, wemust have a mathematical formula which gives thereaction rate

in terms of composition,

temperature,

and pressure of the reaction mixture.

8/10/2019 ERT211 Chp 1-2.pdf

5/27

Enzyme Kinetics

Enzymes are protein catalysts that, like all catalysts,speed up the rate of a chemical reaction withoutbeing used up in the process.

8/10/2019 ERT211 Chp 1-2.pdf

6/27

Enzyme Kinetics

Synthetic catalysts and enzymes use the commontechnique for modeling reaction kinetics.

The rate expressions eventually obtained for both

types of catalysts are very similar and sometimes ofidentical forms.

This is because, in both cases, the reacting moleculesform some sort of complex with the catalyst.

8/10/2019 ERT211 Chp 1-2.pdf

7/27

Enzyme Kinetics

Most synthetic catalysts are not specific; i.e. they willcatalyze similar reactions involving many differentkinds of reactants.

While some enzymes are not very specific, many willcatalyze only one reaction involving only certainsubstrates.

8/10/2019 ERT211 Chp 1-2.pdf

8/27

Explain why enzyme catalysis are nonspecific butenzyme catalysis are specific?

8/10/2019 ERT211 Chp 1-2.pdf

9/27

Define Cofactors

Apoenzyme

Holoenzyme

coenzyme

8/10/2019 ERT211 Chp 1-2.pdf

10/27

Enzyme Kinetic

Enzyme is a catalyst which increases the rate of achemical reaction without undergoing a permanentchemical change.

While a catalyst influences the rate of a chemicalreaction, it does not affect reaction equilibrium.

Equilibrium concentrations can be calculated usingonly the thermodynamic properties of the substrates

and products.

8/10/2019 ERT211 Chp 1-2.pdf

11/27

Enzyme

8/10/2019 ERT211 Chp 1-2.pdf

12/27

Enzyme Kinetics

Both synthetic and biological catalysts can graduallylose activity as they participate in chemical reactions.

However, enzymes are in general far more fragile.

Enzymes contorted shapes in space often endowenzymes with unusual specificity and activity

It is relatively easy to disturb the nativeconformation and destroy the enzyme's catalytic

properties.

8/10/2019 ERT211 Chp 1-2.pdf

13/27

Enzyme Kinetics

It is often asserted that enzymes are more active, i.e.,allow reactions to go faster, than nonbiological catalysts.

At the ambient temperatures where enzymes are mostactive they are able to catalyze reactions faster than themajority of artificial catalysts.

When the reaction temperature is increased, solid(synthetic) catalysts may become as active as enzymes.

The enzyme activity does not increase continuously asthe temperature is raised. Instead, the enzyme usuallyloses activity at quite a low temperature, often onlyslightly above that at which it is typically found.

8/10/2019 ERT211 Chp 1-2.pdf

14/27

8/10/2019 ERT211 Chp 1-2.pdf

15/27

Enzyme reaction rates are determined by severalfactors.

Concentration of substrate molecules

The more of them available, the quicker the enzyme moleculescollide and bind with them).

The concentration of substrate is designated [S] and is expressed in

unit of molarity. Temperature.

As the temperature rises, molecular motion - and hence collisionsbetween enzyme and substrate - speed up.

But as enzymes are proteins, there is an upper limit beyond which

the enzyme becomes denatured and ineffective.

8/10/2019 ERT211 Chp 1-2.pdf

16/27

Enzymes cont.

the presence of inhibitors. competitive inhibitors are molecules that bind

to the same site as the substrate - preventing thesubstrate from binding as they do so - but are not

changed by the enzyme. noncompetitive inhibitors are molecules that

bind to some other site on the enzyme reducing itscatalytic power.

pH. The conformation of a protein is influenced by pHand as enzyme activity is crucially dependent on itsconformation, its activity is likewise affected.

8/10/2019 ERT211 Chp 1-2.pdf

17/27

8/10/2019 ERT211 Chp 1-2.pdf

18/27

How we determine how fast an enzymeworks

We set up a series of tubes containing gradedconcentrations of substrate, [S] . At time zero,we add a fixed amount of the enzymepreparation.

Over the next few minutes, we measure theconcentration of product formed. If theproduct absorbs light, we can easily do this ina spectrophotometer.

Early in the run, when the amount ofsubstrate is in substantial excess to theamount of enzyme, the rate we observe is theinitial velocity ofVi.

8/10/2019 ERT211 Chp 1-2.pdf

19/27

THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION

There is no single theory which accounts for theunusual specificity and activity of enzyme catalysis.

However, there are a number of plausible ideas

supported by experimental evidence for a fewspecific enzymes.

Probably, all or some collection of these phenomenaacting together combine to give enzymes their

special properties.

8/10/2019 ERT211 Chp 1-2.pdf

20/27

THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION

The x-ray crystallography, spectroscopy, andelectron-spin resonance showed the existence of asubstrate-enzyme complex.

The substrate binds to a specific region of theenzyme called the active site,where reaction occursand products are released.

Binding to create the complex is sometimes due to

the type of weak attractive forces.

8/10/2019 ERT211 Chp 1-2.pdf

21/27

THE ENZYME-SUBSTRATECOMPLEX AND ENZYME ACTION

The complex is formed when the substrate key joinswith the enzyme lock.

The hydrogen bonds formed between the substrate

and groups widely separated in the amino acid chainof the enzyme.

8/10/2019 ERT211 Chp 1-2.pdf

22/27

8/10/2019 ERT211 Chp 1-2.pdf

23/27

THE ENZYME-SUBSTRATE COMPLEXAND ENZYME ACTION

The protein molecule is folded in such a way that agroup of reactive amino acid side chains in theenzyme presents a very specific site to the substrate.

The reactive groups encountered in enzymes includethe R group of Asp, Cys, Glu, His, Lys, Met, Ser, Thr,and the end amino and carboxyl functions.

Since the number of such groups near the substrate

is typically 20, only a small fraction of the enzyme isbelieved to participate directly in the enzyme's activesite.

8/10/2019 ERT211 Chp 1-2.pdf

24/27

Large enzymes may have more than one active site.

Many of the remaining amino acids determine thefolding along a chain of amino acids (secondary

structure) and the placement of one part of a foldedchain next to another (tertiary structure), which helpcreate the active site itself

THE ENZYME SUBSTRATE COMPLEX

8/10/2019 ERT211 Chp 1-2.pdf

25/27

THE ENZYME-SUBSTRATE COMPLEXAND ENZYME ACTION

8/10/2019 ERT211 Chp 1-2.pdf

26/27

Enzymes can hold substrates so that their reactiveregions are close to each other and to the enzyme'scatalytic groups.

This feature, which quite logically can accelerate achemical reaction, is known as theproximity effect.

8/10/2019 ERT211 Chp 1-2.pdf

27/27

Reaction will occur only when the molecules come together atthe proper orientation so that the reactive atoms or groups arein close juxtaposition.

Enzymes are believed to bind substrates in especiallyfavorable positions, thereby contributing an orientation effect,

which accelerates the rate of reaction.

Also called orbital steering, this phenomenon has qualitativemerit as a contributing factor to enzyme catalysis. Thequantitative magnitude of its effect, however, is still difficultto assess in general.