For MD, MBBS, BDS & BSc Nursing students

1. Enzymes-II
Prof. (Dr.) Viyatprajna

3. Some Terminologies
Active Site
 Region where substrate binds
 Occupies a very small portion of the enzyme
 Situated in a crevice or a cleft
 During binding specific groups realign themselves to fit
exactly
 Substrate binds by non-covalent bonds
 AA or grs. That directly participate in binding are known
as catalytic residues
 Sometimes catalytic site and substrate binding site may
be different
 Coenzymes and cofactors are a part of the catalytic site
 Serine- frequently present

4. Active site

5. Usually enzymes are larger than their substrates
Exceptions: Proteases, nucleases and amylases

6. Proteases
Serine proteases Trypsin, chymotrypsin,
Clotting factors
Cysteine proteases Papain
Aspartyl proteases Renin, retroviral
proteases, cathepsin
Carboxyl proteases Pepsin
Metalloproteases Carbxypeptidases
Protease inhibitors ACE inhibitor, HIV
(Retonavir)

7. Catalytic efficiency & turnover number
• Most enzyme catalyzed reactions are
highly efficient
• 103 to 108 times faster
• 100-1000 substrate molecules converted
to product every second
• Turnover number- The number of
molecules of substrate converted to
product per enzyme molecule per second

9. Specificity
• Highly specific
• Interacting with one or few substrates
• Catalyze only one reaction

10. Types of specificity
• Absolute specificity
• Group specificity
• Bond specificity
• Stereo specificity

11. Absolute specificity
• Enzyme will act on only one substrate
Glucose Glucokinase Glucose-6-P
Group specificity
Enzymes that act on same reaction in a
group of structurally similar compounds
Ex- Hexokinase acts on glucose, galactose
and mannose

12. Bond specificity
• Specific for a bond- Proteolytic enzymes
Ex- Trypsin can cleave peptide bonds
formed by Arg or Lys in any protein
Stereo specificity
Enzymes showing specificity towards
stereoisomers i.e. they act only on one
type of isomer
Ex- L-LDH will act only on L-lactic acid
and not on D-lactic acid
Human enzymes are specific for L-AA and
D- sugars !!

13. Cofactor/ Coenzyme

14. Cofactor/ Coenzyme
• Holoenzyme → Apoenzyme + Coenzyme
(Active enzyme) (Protein part) (Non-Prot.
part)
• Some enzymes require Metal (Zn, Fe),
organic molecules (coenzymes)
• Inorganic ions- Activators

15. Coenzymes are of 2 types
1. Taking part in reactions catalyzed by
Oxidoreductases e.g.
NAD,FAD,FMN,NADP
2. Taking part in reactions transferring
groups other than hydrogen e.g.
TPP,PLP, CoA, FH4, ATP, Biotin

16. Characteristics of coenzymes
I. When cofactor is some organic substance
II. Group is transferred from or accepted by the
coenzyme
III. Heat stable
IV. Low MW
V. Combine loosely with enzyme
VI. Separated by dialysis
VII. Reaction complete→ Coenzyme released →
Goes to other reaction site

17. Prosthetic group
• When cofactor (collectively includes
coenzymes and metal ions) is strongly
bound to the apoenzyme by covalent or
non-covalent forces
• Ex: PLP, FMN, FAD, TPP, Biotin;
metal ions of Co, Cu, Mg, Mn, Se, and Zn
• Metals are most common
• 1/3rd enzymes contain metals-
Metallozymes /Metallo-enzymes
• Metals as cofactors- Metal activated
enzymes

18. Metallo -enzymes
Metal Metal containing enzyme
Zn Carbonic anhydrase, Carboxypeptidase, ADH
Mg Hexokinase, PFK, Enolase, Glu-6-Phosphatase
Mn Phospho gluco mutase, Hexokinase, Enolase,
Glycosyl transferase
Cu Tyrosinase, cytochrome oxidase, SOD, Lysyl
oxidase
Fe cytochrome oxidase, catalase, peroxidase,
Xanthine oxidase
Ca Lecithinase, lipase
Mo Xanthine oxidase

19. Localization of enzymes
• Intracellular-
Compartmentalization helps in organising
enzymes in a purposeful pathway
Economy of energy
• Extracellular- Secreted out of cell
Ex: α-amylase from salivary glands
Pepsin, renin secreted by gastric glands

20. For more Medical Biochemistry ppt please visit
www.vpacharya.com

21. Enzymology contd………….
He who angers you conquers you.
Elizabeth Kenny