Enzymes mechanism of action, their specificity types, active center structure and action, inhibitor types, fisher and Koshlend theory are presented. Enzymes classification, a new class of enzymes discovered recently, detailed explanation of each class reaction types is presented as well

2. Enzymes, their classification, and
mechanism of action:
coenzymes. Enzymology
Mahira Amirova
Associate Professor
Biochemistry department of
Azerbaijan State Medical University
Year 2021

3. Enzymes, as catalysts, do not affect reaction
equilibrium, but enhance reaction rates by lowering
activation energy and therefore the reaction reaches
equilibrium much faster, when the appropriate enzyme is
present

5. ENZYME ACTION

6. Chemical nature of enzymes
• Enzymes are biological catalysts that
increase the velocity of a chemical
reaction and are not consumed during
reaction.
• Most enzymes are three dimentional
globular proteins (tertiary or
quaternary structure)
• Some RNAs can act like enzymes,
usually catalyzing the cleavage and
synthesis of phosphodiester bonds,
they calls ribozymes.

7. Protein enzymes are classified into 2
types:
Protein enzymes are classified into 2 types:
• 1- Simple enzymes: They are formed of
protein only.
• 2- Complex enzymes (holoenzyme) : They
are formed of protein part and non protein
part:
1) Protein part: called apoenzyme
2) Non- protein: called cofactor
The whole enzyme is called holoenzyme

8. The cofactor is mainly called coenzyme, but actually it can be not coenzyme
only.

9. The cofactor may be coenzyme or prosthetic
group.
 Coenzymes are loosely attached to
enzyme organic, thermo-labile groups.
They are mainly vitamin B derivatives, e.g.
FAD, NAD.
 Prosthetic groups are firmly attached to
enzyme, mostly inorganic, thermo-stable
compounds. They are usually metal ions
e.g. Ca, Zn.

10. Active site
•A short region of an
enzyme molecule which
binds to the substrate
• It is formed from amino
acids sequences (7-15
amino acid residues) in the
polypeptide chain

11. Enzyme active center
• Active center has 2 cites: binding and catalytic
sites:
CATALYTIC
S
Enzyme binds substrate Enzyme makes conversion of substrate

12. • The substrate binds the enzyme, forming an enzyme-
substrate (ES) complex.
• ES is converted to an enzyme-product (EP) complex
that subsequently dissociates to enzyme and product.
E + S ES EP E + P
E-enzyme;S-substrate; P-product;ES and EP-transient
complexes of the enzyme with substrate and with the
product.

13. Fisher theory
• Key and lock:

14. Fisher’s theory key and lock, 1894
The interaction of the substrate and the enzyme is likened to a
key (the substrate) that is highly specific to the lock (the
active site of the enzyme).

15. Koshlend theory: induced deformation

16. Koshland theory induced fit model, 1958
Unlike the lock-and-key model, the induced fit model shows that enzymes
are rather flexible structures in which the active site continually reshapes
by its interactions with the substrate until the time the substrate is
completely bound to it (which is also the point at which the final form and
shape of the enzyme is determined).

17. Specific catalytic groups contribute
to catalysis
General, acid-base catalysis
Covalent catalysis
Nucleophilic-electrophilic catalysis

18. Zymogen (proenzyme)
A zymogen, also called a proenzyme, is an
inactive precursor of an enzyme. A zymogen
requires a biochemical change (such as
a hydrolysis reaction revealing the active site, or
changing the configuration to reveal the active
site) for it to become an active enzyme.
• 1.The digestive enzymes that hydrolyze proteins
are synthesized as zymogens in the stomach and
pancreas and prevent the enzymes from
digesting proteins in the cells in which they are
synthesised
• 2.Blood clotting is mediated by a cascade of
proteolytic activations that ensures a rapid and
amplified response to trauma.

19. PROENZYMES

20. In general, enzymes work in a team, as
complexes

24. OXIDO-REDUCTASES
OXIDATION:
 lose of electron
 lose of proton
 incorporation of oxygen
REDUCTION
 acception of electron
 acception of proton
 lose of oxygen
1. DEHYDROGENASES
2. OXIDASES- pass electrons to O2
3. PEROXIDASES- pass electrons to H2O2
4. OXYGENASES- add O2 TO SUBSTRATE

25. TRANSFERASES
• METHYL-
ACYL-
GLYCOSYL- TRANS-
FERASES
ALDEHYDE-
KETONE-
(transaldolase,
transketolase)
AMINO- TRANSFERASES:
ALAT:
ALANINE PYRUVATE
ASAT:
ASPARTATE
OXALOACETATE

26. LIASES cleave C-C, C-H, C-N, C-P, C-O,
C-S, C-Cl bonds
• HYDRATASE adds H2O
Fumarase incorporates
water into fumarate
FUMARATE
MALATE
• DECARBOXYLASES
remove CO2.
For instance Histidine-
decarboxylase:
PALP
Histidine
HISTAMINE
(has double
bond)
(water added to
double bond spot)
CO2

27. ISOMERASES catalyse intramolecular
changes
 RACEMASES
 TAUTOMERASES
 MUTASES
MUTASE
GLUCOSE-1-PHOSPHATE
GLUCOSE-6-PHOSPHATE
• EPIMERASES
• CIS-TRANS-ISOMERASES
TRIPHOSPHATE-
ISOMERASE:
GAP DAP
(Glyceraldehyde-3-
phosphate)
(Dihydroxyacetone-
phosphate)

28. LIGASES – CHEMICAL COMPOUNDS
are ligated at the expence of ATP
ACETYL-CoA-SYNTHETASE:
Acetate + HS-CoA + ATP
acetyl-CoA +AMP
ACYL-CoA-SYNTHETASE:
Fatty acid + HS-CoA + ATP
acyl-CoA + AMP

29. Specificity
• Absolute specificity
 Absolute substrate specificity- the enzyme will catalyze only on one
substrate in one reaction (urease, arginase etc.)
 Absolute stereochemical specificity - the enzyme will act on a
particular steric or optical isomer of substrate (LDH).
 Absolute substrate group specificity- the enzyme will act only on
molecules that have specific functional groups, such as amino,
phosphate and methyl groups (alcoholdehydrogenase- ADH)
• Relative specificity
 Realative substrate specificity - the enzyme will act on different
molecules but provide the similar types of reactions (cytochrom P450)
 Relative linkage specificity - the enzyme will act on a particular type of
chemical bond regardless of the rest of the molecular structure (pepsin,
trypsin etc.)

30. Specificity of enzymes
Absolute:
*arginase
*urease
*lactate dehydroge-
nase (D-lactate)
*fumarase (trans-)
*oxidase of L- or D-
amino acids
(stereochemical
absolute)
Relative:
*peptidases: pepsin,
trypsin, chymotrypsin,
*glycosidases
*lipase
*cytochrome P450

32. PEPTIDASES or PROTEINASES break
peptides (ptoteins)

33. • Temperature
• Hydrogen ion concentration (pH)
• Concentration of the substrate
• Concentration of the enzyme
• Presence of inhibitors or activators
Factors that affect rate of enzyme
action

35. Effect of temperature
The protein nature of the enzymes makes them extremely
sensitive to thermal changes. Enzyme activity occurs within
a narrow range of temperature compared to ordinary
chemical reactions. As you have seen, each enzyme has a
certain temperature at which it is more active. This point is
called the optimal temperature, which ranges between 37 to
40C°.

36. Temperature affects the enzymes:
• For most enzymes, topt = 20-40 0C.
Exeptions:
• For catalase topt =O 0C.
Adenylate kinase retains its activity at 100 0C.
A temperature rise of 10 0C doubles an activity of enzyme.
Enzymes of glycoprotein nature have higher specificity and are
resistant to temperature.
Hibernation is artifical cooling of body, when the enzymes activity
lowers but can be recovered. Hibernation is used in surgical
interventions incompartable with room temperature action.

38. Effect of pH
Each enzyme has a pH value, that it works at with
maximum efficiency called the optimal pH. If the pH is
lower or higher than the optimal pH, the enzyme activity
decreases until it stops working. For example, pepsin
works at a low pH, i.e, it is highly acidic, while trypsin
works at a high pH, i.e, it is basic. But most enzymes work
at approximately neutral pH 7.4

39. pH:
Weakens or strengthens the connection
between apoenzyme and cofactor
affects the ionization degree of functional
groups in active center
changes the state of activators and inhibitors.

40. Concentration of Enzyme
The rate of an enzyme-catalyzed reaction is directly
dependent on the enzyme concentration. This is true for any
catalyst; the reaction rate increases as the concentration of the
catalyst is increased

41. Enzyme kinetics
Substrate concentration affects the rate of
enzyme-catalyzed reactions. This dependence
of reaction velocity from substrate is presented
by hyperbola.

42. Michaelis-Menten equation
The substrate concentration that results in reaction rate
equal to one-half Vmax is the Michaelis constant Km which
is characteristic for each enzyme acting on a given substare

43. ACTIVATORS of enzymes. Protecting thiol groups
(–SH) compounds from oxidation.

44. Activation by release of non-active
part

45. Activation by partial hydrolysis
Peptide-inhibitor

46. Allosteric activation: formation of
favorable shape of active center
Sfits and
sits

47. INHIBITION OF ENZYMES.
Competitive inhibition
(S)
(I)

48. In non-competitive inhibition inhibitor joins not
to active center or the groups that attach
substrate.

49. Deformation of active site under the
action of allosteric modificator

51. ENZYMES IN BLOOD
SERUM

52. Isoenzymes
Isoenzymes (or isozymes) are multiple forms of same
enzyme, that calalyse the same chemical reaction.
Isoenzymes (also called isozymes) are alternative forms of
the same enzyme activity, that exist in different proportions
in different tissues. Isoenzymes differ in amino acid
composition and sequence and multimeric quaternary
structure; mostly, but not always, they have similar
(conserved) structures. Their expression in a given tissue is a
function of the gene. Each isoenzyme form will have
different kinetic and/or regulatory properties that reflect its
role in that tissue. Isoenzymes are generally identified in the
clinical laboratory by electrophoresis.

53. ISOENZYMES: LDH1, LDH2, LDH3, LDH4,
LDH5
Lactate pyruvate
LDH1 LDH2 LDH3
LDH4 LDH5

54. Tissue distribution of LDH
isoenzymes
Type Composition Location
LDH1 HHHH
Heart and erythrocyte
LDH2 HHHM Heart and erythrocyte
LDH3 HHMM Brain and kidney
LDH4 HMMM Skeletal muscle and
liver
LDH5 MMMM Skeletal muscle and
liver

55. Tissue distribution of API
isoenzymes (Alkaline Phosphatase I)