classification of enzymes and properties of enzymes

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