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CLASSIFICATION OF ENZYMES
TRANSFERASES Transfer of functional groups from one molecule
to another molecule. 5 subclassesTransaminases KinasesTransmethylasesTranspeptidasesTransacylases
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
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
PHOSPHOTRANSFERASES Catalyze transfer of phosphate group Glucose + ATP Glucose-6-P +
ADP TRANSMETHYLASES Catalyze transfer of methyl group
TRANSPEPTIDASES Transfer of amino acid or peptides
TRANSACYLASES Transfer of Acyl groupAcetyl CoA + Choline Acetylcholine+CoA
HYDROLASES Catalyze hydrolysis reactions PROTEIN HYDROLYZING ENZYMES EXOPEPTIDASES POLYPEPTIDASES aminopolypeptidases carboxypolypeptidases
TRIPEPTIDASES DIPEPTIDASES ENDOPEPTIDASES Trypsin, Pepsin,Chymotrypsin,Elastase
CARBOHYDRASES Hydrolysis of glycosidic bond. e.g. Amylase, Maltase, Sucrase, Lactase LIPID HYDROLYZING ENZYMESI. LIPASES act on TAGII. CHOLESTERYL ESTERASE hydrolyze C
– estersIII. PHOSPHOLIPASES act on PL
DEAMINASES adenase Adenine + H2O Hypoxanthine
+ NH3
guanase Guanine + H2O Xanthine + NH3 DEAMIDASES Catalyze hydrolysis of amides. Urea + H2O CO2 +2NH3 Arginine + H2O Ornithine+ Urea
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.
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) .
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.
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
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.
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-CoAAcetyl CoA Malonyl CoA
PROPERTIES OF ENZYMES
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.
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.
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
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
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
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.
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)
DIAGNOSIS OF MI Regulatory proteins involved in myocardial
contractility. Troponin I & Troponin T Enzymes of diagnostic importance CK AST LDH
DIAGNOSIS OF MIENZYME TIME OF
ONSETPEAK 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