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
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
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 !!
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
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