This document defines and provides examples of different types of enzyme regulation, including allosteric enzymes, covalent modulation, and isoenzymes. It discusses how allosteric enzymes have additional sites that allosteric effectors can bind to, inducing a conformational change and activating or inhibiting the enzyme. Covalent modulation involves reversible covalent modifications like phosphorylation regulating enzyme activity. Isoenzymes are multiple forms of the same enzyme that differ in properties and may arise from different genes or subunits. Examples like LDH, CK, and ADH isozymes are provided.

2. Definition: regulates a bio-chem pathway, through its
response to the presence of another bio-molecule.
Ex: hormone production
Types:
1. Allosteric Enzymes
2. Covalent modulation (Latent enzymes)
3. Isoenzymes (LDH, CK, ALP, ADH)

3. Allosteric Sites (AS): additional sites besides active site
Allosteric effectors/modulators (AE): bind at allosteric sie and
regulate enzyme activity
1. Positive AE binds at activator site
2. Negative AE binds at inhibitor site
Classes:
1. K-class
2. V-class

4. Non-covalent reversible binding of AE at the AS brings about a
conformational change in the active site, leading to inhibition or
activation.
Conformational states:
1. T – tense; favored by allosteric inhibitor
2. R – relaxed; favored by substrates
Homotropic effect & Heterotropic effect (+ & -)
Ex:

5. Generally inactive.
Type 1: Proenzymes/zymogens undergo irreversible covalent
activation by the breakdown of 1 or more peptide bonds.
Ex: pepsinogen to pepsin, etc.
Type 2: Interconversion between active and inactive forms by
reversible covalent modifications such as phosphorylation &
dephosphorylation.
• Active when phosphorylated
Ex: Glycongen phophorylase
• Inactive when phosphorylated
Ex: acetyl CoA carboxylase

6. Type 3: Interconversion between active and inactive forms by
reversible covalent modifications such as oxidation and reduction
of disulfide bonds.
Active with sulfhydryl groups (-SH)
Ex: Succinate dehydrogenase

7. Multiple forms of an enzyme catalyzing the same reaction; Differ
in physical and chemical properties.
Possible reasons:
1. Different genes
2. More than one type of sub-units
3. Active as monomer or oligomer
4. Difference in carbohydrate content of a glycoprotein
Ex:
1. LDH (Lactate dehydrogenase)
2. CK (Creatine kinase)
3. ALP (Alkaline phosphatase)
4. ADH (Alcohol dehydrogenase)

8. Oxidoreductase enzyme; catalyzes interconversion of lactate and
pyruvate
Isozymes: LDH1, LDH2, LDH3, LDH4 & LDH5(separated by
electrophoresis). LDH1 being fastest.
Four subunits of two types (M & H)
Significance:
1. LDH1 (H4) pyruvate to Acetyl CoA; aerobic condition
2. LDH5 (M4) pyruvate to lactate; anaerobic condition
Diagnostic imp:
1. Myocardial infarction: LDH1 > LDH2
2. Liver diseases: LDH5 increases

9. Catalyses interconversion of phosphocreatine to creatine


10.  Hydrolase enzyme responsible for removing phosphate groups
Six isozymes based on the differences in carbohydrate content
Diagnostic imp:
1. Hepatitis: increase in alpha2-heat labile ALP
2. Bone diseases: increase in pre beta-ALP

11. Has two heterodimer isozymes:
1. αβ1- Caucasians;
2. αβ2 – Orientals; rapidly converts alcohol to acetaldehyde
This rapid accumulation of acetaldehyde is linked with
tachycardia and facial flushing among Orientals a.k.a. Asian
Flush

12.  Group of ribonucleic acids that function as bio-catalysts
 Ribonuclease p cleaves precursors of tRNAs to give tRNAs; it functions
due to RNA component in it.
 RNA component obey M-M kinetics, exhibited enzyme activity, etc.
 It adapts a tertiary structure (like proteins), which might be the reason
for its catalytic activity.
 Evolutionary significance: ribozymes are believed to function as
catalysts before protein catalysts.

13. Biochemistry by U. Satyanarayana & U.
Chakrapani
Images from the internet