Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st year (First Year) Biochemistry ppt lectures Topic 12 Enzymes Regulation Notes. - biochemistry notes pdf, biochemistry mbbs 1st year notes pdf, biochemistry mbbs notes pdf, biochemistry lecture notes, paramedical biochemistry notes, medical biochemistry pdf, biochemistry lecture notes 2022 ppt, biochemistry pdf.
Enzyme Regulation, 2018
Basic Principles of Metabolic Regulation
Passive: Substrate Availability and
Compartmentation
Active: Regulation of Rate Limiting Enzyme
Substrate availability and Compartmentation
? Passive mechanism
? Limited capacity
? Anabolic and Catabolic pathways separated
E.g. Fatty acid synthesis & Fatty acid oxidation
? Specialized subcellular compartments (Hydrolases in Lysosomes)
Controlling Rate Limiting Enzyme
Regulation of
? Regulation of Enzyme
Enzyme quantity
synthesis
Regulation of
? Al osteric Regulation
Enzyme catalytic
activity
? Covalent Modification
Regulation of enzyme synthesis
? Gene Transcription induction and Repression
? HMG-CoA reductase by cholesterol
? PEP carboxykinase by insulin and glucagon
? Cytochrome P450 by various drugs
? Slow Process
? Long Term Effect
Regulation of enzyme catalytic activity
Allosteric Regulation
? Within seconds
? Allosteric Enzymes: Catalysis at active site modulated
by presence of effector at allosteric site
? Positive or negative effectors
? May affect affinity (K series) or
? Catalytic activity (V series)
Homotropic or Heterotropic effectors
? Homotropic:
? Heterotropic
? Substrate itself an effector
? Effector different from
? Mostly, Positive effector
substrate
? Exhibit cooperativity
? Feedback inhibition
? Hyperbolic curve
? Hills equation define
characteristics
Examples of allosteric regulation
? Most of the rate limiting steps in metabolic pathways
? Feedback inhibitions
? Phosphofructokinase
? Aspartate transcarbamoylase
? Which of the following describes a characteristic of
most allosteric enzymes?
? (A) They are composed of single subunits.
? (B) They show cooperativity in substrate binding.
? (C) They have allosteric activators that bind in the catalytic site.
? (D) They have irreversible allosteric inhibitors that bind at allosteric
sites.
Covalent modification
Partial Proteolysis
Phosphorylation
Partial proteolysis
? Proteases synthesized as inactive precursor:
Proproteins/Proenzymes/Zymogens
? Eg. Pepsin, Tr ypsin, Chymotrypsin, Clotting factors
? Irreversible modification
? Selective Proteolysis leads to conformation change and
configures active site
Phosphorylation/Dephosphorylation
? Catalysed by Protein kinases and Phosphoprotein phosphatases
? Act on serine, threonine and tyrosine residues
? May increase or decrease activity
Example
? High Insulin/Glucagon Ratio decreases c AMP and Protein kinase
A causing dephosphorylation of PFK-2 (Active)
? Active PFK2 increases Fructose 2,6-bisphosphate that increases
PFK-1 activity causing increased glycolysis
? Reverse happens under the effect of glucagon that increases
phosphorylation by in increasing c AMP
Phosphorylation/Dephosphorylation
? Most common mechanism employed for regulation
? Ease of interconversion
? Chemical nature of phosphoryl group helps in conformational changes of
enzymes
? H bond formation by O
? Negative charge
? Insulin/ Glucagon hormones regulates enzymes
Summary
Enzyme
Regulation
Active:
Passive:
Regulation
substrate
of Enzyme
availability/Co
activity
mpartmentatio
n
Enzyme
Allosteric
Covalent
Synthesis
Regulation
Modification
References
? Victor W. Rodwell, David A. Bender, Kathleen M. Botham, Peter J. Kennelly,
P. Anthony Weil. Harper's Illustrated Biochemistry, 30th Edition
? Denise R. Ferrier; Lippincott Illustrated Reviews Biochemistr y, 7th Edition
Thank You!
This post was last modified on 05 April 2022