classification of enzymes into 6 major classes and then into minor sub-classes , properties

2. TRANSFERASES
Transfer of functional groups from one molecule to
another molecule.
5 subclasses
 Transaminases
 Kinases
 Transmethylases
 Transpeptidases
 Transacylases

3. TRANSAMINASES
Catalyze exchange of –NH2 group b/w amino acid & keto
acid.
COOH COOH COOH COOH
│ │ │ │
H2NCH C=O AST C=O H2NCH
│ + │ │ + │
CH2 CH2 CH2 CH2
│ │ │ │
CH2 COOH CH2 COOH
│ │
COOH COOH
G.A OAA αKG AA

4. COOH COOH COOH COOH
│ │ ALT │ │
H2NCH + C=O C=O + H2NCH
│ │ │ │
CH2 CH3 CH2 CH3
│ │
CH2 CH2
│ │
COOH COOH
G.A PA α KG ALANINE
TRANSAMINASES

5. PHOSPHOTRANSFERASES
Catalyze transfer of phosphate group
Glucose + ATP Glucose-6-P + ADP
TRANSMETHYLASES
Catalyze transfer of methyl group

6. TRANSPEPTIDASES
Transfer of amino acid or peptides
TRANSACYLASES
Transfer of Acyl group
 Acetyl CoA + Choline Acetylcholine+CoA

7. HYDROLASES
Catalyze hydrolysis reactions
PROTEIN HYDROLYZING ENZYMES
EXOPEPTIDASES
 POLYPEPTIDASES aminopolypeptidases
carboxypolypeptidases
 TRIPEPTIDASES
 DIPEPTIDASES
ENDOPEPTIDASES
Trypsin, Pepsin,Chymotrypsin,Elastase

8. CARBOHYDRASES
Hydrolysis of glycosidic bond.
e.g. Amylase, Maltase, Sucrase, Lactase
LIPID HYDROLYZING ENZYMES
I. LIPASES act on TAG
II. CHOLESTERYL ESTERASE hydrolyze C – esters
III. PHOSPHOLIPASES act on PL

9. DEAMINASES
adenase
Adenine + H2O Hypoxanthine + NH3
guanase
Guanine + H2O Xanthine + NH3
DEAMIDASES
Catalyze hydrolysis of amides.
Urea + H2O CO2 +2NH3
Arginine + H2O Ornithine+ Urea

10. OTHER ESTER HYDROLYZING ENZYMES
PHOSPHATASES
 PHOSPHOMONOESTERASES
e.g. Acid phosphatase , alkaline phosphatase
G-6-P + H2O Glucose + Phosphoric acid
 PHOSPHODIESTERASES
Splits off one phosphate group of diesters.

11.  PHOSPHORYLASES
Add inorganic phosphate (Pi) to split bond.
glycogen phosphorylase
Glycogen + H3PO4 Glucose I-P
 PYROPHOSPHATASES
Hydrolyze pyrophosphates(PPi)
PPi +H2O 2Pi
 NUCLEASES
Decompose nucleic acid.( polynucleotides to
mononucleotides) .

12.  NUCLEOTIDASES
Hydrolyze mononucleotides to nucleosides & H3PO4.
 NUCLEOSIDASES
Nucleoside + H3PO4 free nitrogen base +
sugar phosphate
MISCELLANEOUS
 CHOLINESTERASE
acetylcholine to acetic acid & Choline.
 SULFATASE
Catalyze hydrolysis of sulfate esters.

13. LYASES
Catalyze addition of NH3, H2O, CO2 to double bond or
their removal from double bond.
COOH COOH
│ fumarase │
CH + H2O HOCH
║ │
HC CH2
│ │
COOH COOH
Fumaric acid Malic acid

14. ISOMERASES
Catalyze structural change within a single molecule by
transfer of group within it resulting in formation of an
isomeric form of the substrate.
phosphohexose isomerase
Glucose-6-P Fructose 6-P
e.g.
racemases,epimerases,cis-trans isomerases.

15. LIGASES
Catalyze condensation reactions joining two molecules by
forming C-O, C-S, C-N, C-C bonds along with energy
releasing hydrolysis or cleavage of high energy phosphates.
CH3 Acetyl CoA COOH
│ carboxylase │
C=O + CO2 +ATP CH2 + ADP + Pi
│ │
S-CoA C=O
│
S-CoA
Acetyl CoA Malonyl CoA

16. PROPERTIES OF ENZYMES

17. 1. SPECIFICITY
Specific in their action though to a variable extent.
 ABSOLUTE SPECIFICITY
CA
CO2 + H2O H2CO3
 RELATIVE SPECIFICITY
Pancreatic esterase; hydrolyze both aliphatic esters &
Cholesteryl esters.

18.  BOND SPECIFICITY
TRYPSIN; hydrolyze residue of only lysine & arginine.
LIPASES; hydrolyze ester bond.
 GROUP SPECIFICITY
one enzyme catalyze same reaction on a group of structurally
similar compounds.
HEXOKINASE; catalyze Phosphorylation of
glucose,fructose,mannose.
 STEREOSPECIFICITY
Enzymes distinguish b/w D-& L-sugars as well as D-& L-
amino acids.

19. 2. PROTEIN NATURE
Enzymes are protein in nature
Except few RNAs
3. DIRECTION OF ENZYME REACTION
BIDIRECTIONAL
A + B C + D
UNIDIRECTIONAL
A + B C + D

20. 4.PROENZYMES
 Inactive form of enzymes.
 Active site of enzyme is masked by a small region of
peptide chain that is removed by hydrolysis of specific
bond.
 Prevent autolysis of cellular structural proteins.
e.g. Pepsinogen ; pepsin by gastric HCL
Trypsinogen ; trypsin
5.ENZYME LOCATION
Cytosol ; F.A synthesis
Mitochondria ; F.A oxidation

21. 6.ENZYMES CATALYZING RATE - LIMITING
REACTIONS
Enzyme catalytic efficiency determines efficiency of an entire
metabolic reaction.
HMG-CoA reductase cholesterol synthesis
↓
statin drugs inhibit it.
7.ENZYME INDUCTION
Enzymes previously absent or present only in traces in certain
microorganisms can be induced by substances called INDUCERS,
which in many cases are actual substrates.
e.g. Induction of penicillanase by penicillin in bacteria

22.  Phenobarbitone induces synthesis of many hepatic
microsomal enzymes including bilirubin glucuronyl
transferase.
 Barbiturates ↑ δ ALA synthetase & precipitates acute
intermittent porphyria.
8.ENZYME REPRESSION
 INSULIN induces enzymes of glycolysis
 GLUCAGON represses them
 E.COLI make tryptophan synthetase when medium
doesn't contain tryptophan.

23. 9.ISOZYMES
Physically distinct version of a given enzyme, each of which
catalyze the same reaction.
LDH , 5 isozymes
LDH I HHHH (heart)
LDH 2 HHHM
LDH3 HHMM
LDH4 HMMM
LDH5 MMMM (muscles)
CK , 3 isozymes
CK 1 BB (brain)
CK 2 BM (heart)
CK 3 MM (sk. Muscles)

24. DIAGNOSIS OF MI
 Regulatory proteins involved in myocardial contractility.
Troponin I & Troponin T
 Enzymes of diagnostic importance
CK
AST
LDH

25. DIAGNOSIS OF MI
ENZYME TIME OF
ONSET
PEAK LEVEL DURATION OF
RISE
TROPONIN I 4-6 hr 8-24 hr 3-10days
CK-MB 4-8hr 12-24hr 48-72hr
AST 6-8hr 24-48hr 3-5days
LDH 12-24hr 48-72hr 7-12days