Enzymes

An enzymes can be defined as a protein produced by living cells, which is capable of catalysing a chemical reaction to yield specific products in other words, an enzyme is a biological catalyst. Their role is very large. So, academic Pavlov was saying: “ The enzymes are the center of biological and medical knowledge “. Braunsthein said: “All modern biochemistry speaks on enzyme’s language”.

The word enzyme means “derived from yeast” and was used when the catalytic properties of the yeast were discovered. A catalyst is an agent which in small amounts increases the velocity of a reaction without appearing in the final products of the reaction.

The substance on which an enzyme acts is called its substrate. The names of enzymes usually end is “ase” which is preceded by the name of its substrate. Many enzymes have been crystallized in pure form (now near 2500): urease was the first enzyme to be crystallized in 1926 by Sumner. The enzymes can bring about chemical reaction in body tissues or even in vitro at comparatively low temperature and low dilutions.

Mechanism of enzyme action

Enzymes decrease the energy of activation of reaction by the way of the formation enzyme-substrate complex. The velocity of reaction depends on the quantity of molecules, which level of free energy of activation more than energetic barrier. So, 2H2O2à2H2O + O2/ the energy of activation of this reaction is 75 kJ/mol. When Pt is used as catalyst the level of energy of activation of this reaction is decreased and equal 54kJ/mol. When the enzyme catalyze this reaction the energy of activation is decreased and equal 18kJ/mol.

The formation of enzyme-substrate complex

There are 3 steps in this process –

1. The formation of complex enzyme-substrate (by the weak bonds)

2. the occurrence of reaction with substrate (cleavage or formation of bonds< formation of products), formation of complex enzyme-products of reaction

3. the discharge of products from enzyme

Common properties of enzymes

There are 5 differences or general properties of enzymes:

a) A complicity structure of enzymes

b) The enzymes are compounds which have a high proper of action, or high activity

c) The enzymes have specificity

d) The enzymes act in physiologic conditions, for example in temperature about 37 and neutral pH

e) The enzymes are compounds with regulated activity and different factors act on they activity, t, pH, effectors, concentration of substrates and enzymes.

The complicity of structure of enzymes.

There are one- component enzymes and two – component enzymes

One- component enzymes or simple are simple proteins, but they differ from simple proteins by the presence of active centre. Active centre is a functional group of amino acids occurred in space. Active centre has got next sites:

• Substrate site – “the hand of enzymes” or contactive site, or anchors place. This site stipulates substrates specificity of enzymes;

• Catalytic site which responsible for chemical reaction.

This site stipulates a specificity of action of enzymes. Some of enzymes have a quaternary structure a do the allosteric centers. The allosteric centre takes part in regulation of activity of enzymes. Almost all of enzymes of gastrointestinal tract are one- component.

Two- components enzymes are built as conjugated proteins. They consist of proteins part, or apoenzyme and non- proteins part, or coenzyme. Apoenzymes stipulate a substrates specifyty; coenzyme promotes specificity of action. The composition of coenzyme may be vitamins or metals. Some of two- components enzymes have a durable bond between apo-and coenzyme.

Some two- component enzymes have got an isoforms “isoenzyme”. Isoenzyme act the substrate catalyzed some reactions. Isoenzyme has the some coenzymes, but differs from each other by the structure of apoenzyme. Isoenzyme occurs in a certain tissues.

This property of isoenzyme is named “organo specificity” and pays very important role in diagnosis test.

For example, enzyme lactate dehydrogenase has got 5 (5 isoforms) isoenzyme.

LDG-1- heart

LDG-2- kidneys

LDG-3- lung

LDG-4- liver

LDG-5- liver

In the damage of some organs the LDG exist into the blood and its concentration in blood is increase. In physiologic conditions the level of LDG equal 5 units and relationships between isoenzymes is next LDG_-1,3 : LDG-_4,5 (4.0 : 6,0). In pathological conditions the level of LDG is increased . If the damage of heart or lung the level of LDG-1,3 is increase and the relationships between LDG isoforms is next: LDG_-1,3 : LDG-_4,5

50 : 50

or 60 : 40

If the damage of liver is observed the level of LDG_- is increased and the relation ship between LDG- isoenzymes is next: LDG_-1,3 : LDG-_4,5

30 : 70

20 : 80

The next property of enzymes is high activity. The activity of enzymes is measured in catal. Catal – is a quantity of molecular f substrate on which the molecule enzyme acts during 1 m/n. f.ex: enzymes catalase has got activity 1 m/in catal, if means that the 1 molecule of catalase acts on 1 m/n of its substrate during 1 min.

The next property of enzymes is specificity. There are 2 types of enzymatic specificity

Specificity

S ubstrate specificity Specificity of action

Absolute stereo chemical relative

Substrate specificity is named “absolute” were the enzymes acts on one substrate only, f.e. maltase acts on maltose, only.

Substrate specificity is named “relative” when the enzyme acts on the group of substrates, which have the same type of linkage, f.e α- amylase acts on starch and glycogen. These substrates have the same type of linkage.

Substrate specificity is named “stereo chemical” when the enzymes catalyzed the reaction with one from possible stero isomers of substrate f.e. enzyme fumarathydrotase catalyzed the hydration of fumarate and doesn’t act on maleniate. Fumarate and maleniate are stereoisomers of gulantadioic acid. Fumarate is trans –isomers, maleniate- is a cys- isomer.

The specificity of action of enzymes is an ability of enzymes to catalyzed specific reaction. The enzymes many possess the same substrates specificity, but each from them catalyzed only specific reaction with substrate, f.e. multienzymatic complex in which the enzymes act, but each of them catalyzed the specific reaction, f.e pyruvate dehydrogenase complex has got at least 3 enzymes:

-pyruvate dehydrogenase (PDH)

- pyruvate decarboxylases (PDC)

- acetyltransferase (HSCoA)