Composition of enzymes

Simple enzymes: enzymes composed only of amino acid residues.

Bound enzymes: composed of enzyme proteins and non-protein cofactors

Enzyme protein: determines the specificity of the reaction;

Cofactors: determine the type and nature of the reaction; can be metal ions or small organic compounds.

 

Cofactors

Cofactor: loosely bound to enzyme protein, can be removed by dialysis or ultrafiltration.

Cofactor: tightly bound to enzyme protein, cannot be removed by dialysis or ultrafiltration.

The complex formed by the combination of enzyme protein and cofactor is called holoenzyme, and only holoenzyme has catalytic effect.

 

The active centre of enzyme

①Enzyme necessary groups: necessary for the enzyme to play the activity of the group

② the active centre of the enzyme: in the primary structure is very far apart, but in the spatial structure of some of the R groups close to each other to form a special region, the region can specifically bind the substrate and catalyze the substrate to undergo chemical changes.

The active centre must groups are divided into:

Binding groups: involved in enzyme-substrate binding

Catalytic groups: catalyse the transformation of substrates into products.

Required groups outside the active centre: there must be a required group within the active centre, but the required group may not always be in the active centre. The mandatory group outside the active centre serves to stabilise the active centre.

 

Difference between enzyme and general catalyst

① high efficiency: the catalytic effect of the enzyme can increase the reaction rate of 10^6 to 10^12 times, before and after the reaction of the enzyme itself does not change, high efficiency is to reduce the activation energy of the reaction

②Specificity (selectivity for substrate)

Ⅰ absolute specificity: the enzyme is very strict on the substrate requirements, only a specific substrate;

Ⅱ relative specificity: the object of action is not a substrate, but a class of compounds or chemical bonds;

Ⅲ stereoisomer specificity: D-, L-, cis-trans

③ Enzyme activity instability: proteins are easily denatured and inactivated

④Enzyme activity can be regulated and controlled: Ⅰ allosteric regulation; Ⅱ feedback regulation; Ⅲ valence-dependent modification regulation; Ⅳ zymogen activation and hormone control

 

Doctrine of induced fit

The enzyme surface does not have a fixed shape that is complementary to the substrate, but only forms a complementary shape due to the induction of the substrate.

 

Factors affecting the enzymatic reaction

(1) substrate concentration; (2) inhibitor; (3) enzyme concentration; (4) temperature; (5) pH; (6) activator.

 

The effect of substrate concentration on the rate of enzymatic reaction:

Intermediate product doctrine: when enzyme catalysis, the enzyme active centre first combines with the enzyme substrate to form a complex of an enzyme and a substrate, which then decomposes to release the enzyme and releases the products

Mie’s equation: V=Vmax×[S]/(Km+[S])

(1) When the substrate concentration is very large ([S]≥10×Km), the enzyme is saturated with the substrate, and the reaction rate reaches the maximum.

(2) When the reaction velocity V=1/2Vmax, Km=[S].

The significance of the kinetic parameter Km in Mie’s equation★

①Km is numerically equal to the substrate concentration corresponding to half of the maximum reaction rate, i.e., when V=1/2Vmax, Km=[S]

②Km unit: mol/L

③ different enzymes have different Km values, which is an important characteristic physical constant of enzymes

The same enzyme has different Km values for different substrates, and the substrate with the smallest Km is called the most suitable substrate.

⑤ Km indicates the degree of affinity between the enzyme and the substrate: the larger the Km value, the smaller the affinity and the lower the catalytic activity; the smaller the Km value, the larger the affinity and the higher the catalytic activity

 

The effect of inhibitors on the rate of enzymatic reaction

(1) Irreversible inhibition

Inhibitors and the active group of the enzyme activity centre or some of the groups in its site in the form of covalent binding, causing enzyme inactivation, physical methods can not be eliminated

 

(2) Reversible inhibition

Ⅰ Competitive inhibition

a. The chemical structure of the inhibitor is similar to that of the substrate, which can competitively bind to the enzyme active centre with the substrate;

b.When the inhibitor binds to the active centre, the substrate is excluded from the reaction centre, with the result that the enzymatic reaction is inhibited;

c. Increasing the concentration of the substrate increases the ability of the substrate to compete (i.e., it can release the inhibition);

d. the Km value rises and the Vmax remains constant

 

II Non-competitive inhibition

Binding to a mandatory group other than the active centre

Km value remains unchanged, Vmax decreases

 

Ⅲ anticompetitive inhibition

Binding to enzyme-substrate complex

Km value decreases, Vmax decreases

 

Activation of zymogen

①Enzymogen: inactive enzyme precursor

②Activation: primary structure change, causing conformational change, formation or exposure of active centre

 

Enzyme activity regulation

① covalent modification of enzymes (chemical modification regulation): an enzyme is modified by another enzyme, covalently attached to a chemical group, or covalent bond breaking, remove a chemical group, thereby regulating the activity of enzymes

② allosteric regulation: some substances can be reversibly bound to the active centre of the corresponding enzyme molecule or a specific part of the molecule other than the active centre, so that the enzyme’s active centre conformation changes, resulting in functional changes

 

Isoenzyme

① refers to the catalytic chemical reaction is the same, the enzyme protein molecular structure, physical and chemical properties and immunological properties of a group of different enzymes ② this kind of enzyme exists in the same species of organisms or the same body of different tissues or even the same tissue or cells

 

Trypsin as an example of the relationship between protein structure and function

Because trypsin is far apart in the primary structure, enterokinase cuts the N-terminal 6 peptide, so that its primary conformation changes, forming a special region, that is, the active centre of the enzyme, the region can specifically bind the substrate and catalyse the substrate to undergo a chemical change, playing a binding and catalytic function, explaining the change in the primary structure, causing a change in the conformation, the formation of the active centre, so that the tryptic protein from inactive to active.

Contact Us Now!

If you need Price, please fill in your contact information in the form below, we will usually contact you within 24 hours. You could also email me info@longchangchemical.com during working hours ( 8:30 am to 6:00 pm UTC+8 Mon.~Sat. ) or use the website live chat to get prompt reply.

Compound Glucoamylase	9032-08-0
Pullulanase	9075-68-7
Xylanase	37278-89-0
Cellulase	9012-54-8
Naringinase	9068-31-9
β-Amylase	9000-91-3
Glucose oxidase	9001-37-0
alpha-Amylase	9000-90-2
Pectinase	9032-75-1
Peroxidase	9003-99-0
Lipase	9001-62-1
Catalase	9001-05-2
TANNASE	9025-71-2
Elastase	39445-21-1
Urease	9002-13-5
DEXTRANASE	9025-70-1
L-Lactic dehydrogenase	9001-60-9
Dehydrogenase malate	9001-64-3
Cholesterol oxidase	9028-76-6