Enzymes play a crucial role in various biological processes. They are responsible for catalyzing the chemical reactions that occur in living organisms, including those involved in metabolism. Moreover defects in enzyme function can lead to various medical conditions, including genetic disorders and diseases caused by environmental factors.
Understanding the role of enzymes in metabolic pathways is critical for understanding how the body functions at a molecular level.
Let’s learn some more about this
important topic of biochemistry through this blog below.
Enzymes are proteins except ribozymes in which RNA acts as enzyme.
Protein breaking enzyme
Aspartate & Histidine are present at binding site for substrate
Serine is present at catalytic site and is responsible for cutting the substrate
e.g. Chymotrypsin, Trypsin, elastase, plasmin, thrombin, clotting factor 10 & 11 and prostate specific Antigen
These serine proteases have a role in tumor cell metastasis.
Chymotrypsin cuts at C- terminal of large hydrophobic amino acids like Phe, Tyr and Trp
Trypsin cuts at carboxy terminal of basic amino acids like Lys and Arg
Elastase cuts at carboxy terminal of small neutral amino acids e.g. glycine, serine.
Michaelis Menten Graph (Most Enzymes)
For simple or most of the enzymes.
m is defined as that substrate concentration at which velocity of reaction is half of V max K
m can't be equal to V max /2 (as the units of two parameters are different) K
m is signature of Enzyme as It is constant value for a particular enzyme K
m does not change with change in either enzyme or substrate concentration Km 1affinity , So, in case of competitive inhibition affinity↓ so K
Graph for Allosteric or regulatory Enzymes (Few Enzymes)
Have active site + regulatory/allosteric site
regulator (activator or inhibitor) binds to allosteric site
V vs is Sigmoidal/S shape graph
Temperature & pH Graph: Bell Shaped Graph
At extremes of temp/ pH, proteins/enzymes are denatured, so, velocity is negligible
Velocity is max at optimum temp and pH only Optimum temp is 37
o C and optimum pH is 5-9 for human enzymes
Enzyme Class (EC no.)
Use O2 as an electron acceptor like cyt C Oxidase
Use molecules other than O2 as electron acceptor (NAD, FAD, NADP); e.g. PDH in link reaction.
Use H2O2 as electron acceptor; e.g., Glutathione peroxidase
Incorporate O2 into the substrate; 2 types:
Dioxygenase: incorporates 2 atoms of molecular o2 into the substrate e.g. homogentisate dioxygenase
Monooxygenases/Hydroxylases/mixed function oxidases: incorporates 1 atom of molecular O2 into the substrate. e.g. phenylalanine hydroxylase (converts Phe to Tyr)
Example: Glutathione reductase
Transfer one carbon units
Transfer amino groups
Transfer phosphate from ATP
Transfer phosphate Pi
All digestive enzymes
Remove phosphate from a substrate using water
any enzyme that breaks macromolecule e.g. amylase, maltase etc.
Aldolase A & B
Link 2 molecules without using ATP
Produce aldehydes via elimination reactions
Produce CO2 via elimination reactions
Add or remove water but do not break bond e.g. Enolase, aconitase, fumarase, PEPCK
Interconvert L & D stereoisomers
Transfer group b/w atoms within a molecule
Link 2 molecule via an ATP-dependent
Use ATP, Biotin and CO2 (Mn- ABC) and also uses Mg2+
Oxidases which do not require copper: Xanthine oxidase and Sulfite oxidase
Type of Inhibition Km Vmax Competitive Increased Same Non-Competitive Same Decreased Un-Competitive Decreased Decreased
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ELECTROPHORETIC MOBILITY OF ISOENZYMES
Isozyme number is inversely related to mobility. i.e.
Least number → moves maximum
Highest number → moves least
In five LDH isoenzymes, LDH-1 moves max and LDH-5 moves least
Out of 3 isoenzymes of CK, CK-1 moves max and CK-3 moves least
PROPERTIES OF ENZYMES
↑ velocity/rate of reaction
↓ Activation energy
Do not change the equilibrium of reaction
Do not change the free energy of substrates/products
Previous Year’s Question
Q. Identify the type of inhibitor in the graph?(INICET May 2022)
Competitive inhibitor Non-competitive inhibitor
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