Explain second and third answer for pharm d student 1st year

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Question 2: Factors Affecting Enzyme Activity + Properties of Enzymes

Properties of Enzymes

Before diving into factors, here are the key properties of enzymes you need to know:

Property	Explanation
Proteins	All enzymes are proteins (except ribozymes — RNA-based).
Catalysts	Speed up reactions without being consumed or permanently changed.
Specificity	Each enzyme acts on only one or a few specific substrates (binding specificity).
Reaction specificity	Catalyze only one type of reaction — no by-products.
Stereospecificity	Recognize only one enantiomeric (mirror image) form of a substrate (e.g., proteases act only on L-amino acids).
Do NOT shift equilibrium	They speed up reaching equilibrium but don't change the equilibrium constant (Keq).
Regulated	Activity is controlled by allosteric molecules, inhibitors, or covalent modification.

— Henry's Clinical Diagnosis and Management by Laboratory Methods

Factors Affecting Enzyme Activity

1. Temperature

Every 10°C rise in temperature approximately doubles enzyme activity (Q10 effect).
However, high temperatures cause denaturation — enzymes lose their 3D shape and activity.
- Example: Creatine kinase (CK) denatures at 37°C; amylase at 45°C.
Exception: Taq polymerase remains stable at 95°C (used in PCR).
Low temperatures slow reactions but preserve enzyme stability — useful for storing samples.

2. pH

Each enzyme has an optimal pH at which it works best.
- Pepsin (stomach): optimal pH ~2 (acidic)
- Trypsin (small intestine): optimal pH ~8 (slightly alkaline)
- Most body enzymes: optimal pH ~7.4
pH affects the ionization of amino acids in the active site, changing enzyme shape and substrate binding. Extreme pH causes denaturation.

3. Substrate Concentration ([S])

As [S] increases, reaction velocity (v) increases — more enzyme-substrate complexes form.
At very high [S], the enzyme becomes saturated and velocity reaches a maximum (V~~max~~).
This relationship follows Michaelis-Menten kinetics: the Km (Michaelis constant) is the [S] at which velocity = ½ V~~max~~. A lower Km means higher affinity for the substrate.

4. Enzyme Concentration

If substrate is in excess, reaction rate is directly proportional to enzyme concentration — more enzyme molecules = more active sites = faster reaction.

5. Cofactors and Coenzymes

Many enzymes require non-protein helpers:
- Cofactors: inorganic ions (Mg²⁺, Zn²⁺, Fe²⁺)
- Coenzymes: organic molecules (NAD⁺, FAD, Coenzyme A — most derived from vitamins)

6. Inhibitors (see Question 3 below)

Question 3: Enzyme Inhibition — Definition and Types

Definition

Any substance that decreases the velocity of an enzyme-catalyzed reaction is called an inhibitor.

Types of Enzyme Inhibition

A. Irreversible Inhibition

Inhibitor binds to the enzyme via a covalent bond — permanent, cannot be reversed by dilution.
Destroys enzyme function permanently.
Example: Lead (Pb²⁺) irreversibly inhibits ferrochelatase (an enzyme in heme synthesis) by forming covalent bonds with cysteine's –SH group.
Aspirin irreversibly inhibits cyclooxygenase (COX), blocking prostaglandin synthesis.

B. Reversible Inhibition

Inhibitor binds via non-covalent bonds — can be removed by dilution. Two main types:

1. Competitive Inhibition

The inhibitor looks like the substrate and competes for the same active site.
Substrate and inhibitor cannot bind simultaneously.

Parameter	Effect
V~~max~~	Unchanged — can be overcome by adding excess substrate
Km	Increased (apparent) — more substrate needed to reach ½ V~~max~~

Lineweaver-Burk plot: Lines intersect on the y-axis (same 1/V~~max~~, different x-intercepts).

Competitive inhibition — Vmax unchanged, Km increased

Pharma example: Statins (e.g., pravastatin, atorvastatin) competitively inhibit HMG-CoA reductase, blocking cholesterol synthesis. Methotrexate competitively inhibits dihydrofolate reductase (DHFR).

2. Noncompetitive Inhibition

The inhibitor binds to a different site (allosteric site) — not the active site.
Can bind to free enzyme OR the enzyme-substrate (ES) complex.
Substrate binding is unaffected, but the reaction cannot proceed normally.

Parameter	Effect
V~~max~~	Decreased — cannot be overcome by adding more substrate
Km	Unchanged — substrate affinity is unaffected

Lineweaver-Burk plot: Lines intersect on the x-axis (same –1/Km, different y-intercepts).

Noncompetitive inhibition — Vmax decreased, Km unchanged

Example: Heavy metals like Hg²⁺ acting on –SH groups away from the active site.

3. Uncompetitive Inhibition

Inhibitor binds only to the ES complex (not free enzyme).
Both V~~max~~ and Km are decreased proportionally.
Lineweaver-Burk plot: Parallel lines (same slope, different intercepts).

Quick Comparison Table

Feature	Competitive	Noncompetitive	Uncompetitive
Binding site	Active site	Allosteric site	ES complex only
V~~max~~	Unchanged	Decreased	Decreased
Km	Increased	Unchanged	Decreased
Reversible by excess [S]?	Yes	No	No
Lineweaver-Burk	Same y-intercept	Same x-intercept	Parallel lines

Drug Examples (Important for Pharm D)

Drug	Mechanism
Statins (atorvastatin)	Competitive inhibition of HMG-CoA reductase
Penicillin / Amoxicillin	Irreversible inhibition of bacterial cell wall synthesis enzymes
ACE inhibitors (captopril, enalapril)	Inhibit angiotensin-converting enzyme → vasodilation
Aspirin	Irreversible inhibition of COX (cyclooxygenase)
Methotrexate	Competitive inhibition of DHFR

Sources: Lippincott's Illustrated Reviews Biochemistry 8th ed.; Henry's Clinical Diagnosis and Management by Laboratory Methods

Explain the factor affecting enzyme activity. Add a note on the properites of enzymes for pharm d 1st year

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factors affecting enzyme activity pH temperature substrate concentration graph

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Factors Affecting Enzyme Activity + Properties of Enzymes

(Pharm D 1st Year — Biochemistry)

PART 1: FACTORS AFFECTING ENZYME ACTIVITY

Enzyme activity refers to the rate at which an enzyme catalyzes its reaction. Several factors can increase or decrease this rate:

1. 🌡️ Temperature

Enzyme activity increases as temperature rises — generally, every 10°C increase doubles the reaction rate (Q₁₀ effect).
This is because higher temperature increases molecular kinetic energy, leading to more frequent enzyme-substrate collisions.
However, above an optimal temperature, the enzyme begins to denature — its 3D structure unfolds, active site is destroyed, and activity drops sharply to zero.

Key examples:

Enzyme	Starts to Denature At
Creatine Kinase (CK)	37°C
Amylase	45°C
Taq Polymerase	Stable up to 95°C (used in PCR)

Practical note: Clinical lab samples stored at 4°C remain stable for ~1 week. Deeper freezing (−80°C) preserves enzyme activity longer.

2. 🧪 pH

Every enzyme has an optimum pH at which it shows maximum activity.
Changes in pH affect the ionization of amino acid residues in the active site, altering the enzyme's shape and ability to bind substrate.
Extreme pH values on either side cause denaturation.

Key examples:

Enzyme	Optimal pH	Location
Pepsin	~2 (acidic)	Stomach
Trypsin	~8 (basic)	Small intestine
Alkaline Phosphatase (ALP)	9–10	Liver/bone
Most body enzymes	~7.4	Blood/cytoplasm

3. 📊 Substrate Concentration [S]

As substrate concentration increases, reaction velocity (v) increases — more substrates fill available active sites.
At very high [S], all active sites are occupied → the enzyme is saturated → velocity reaches a maximum (V~~max~~).
This follows Michaelis-Menten kinetics:

$$v_0 = \frac{V_{max}[S]}{K_m + [S]}$$

Km (Michaelis constant) = the [S] at which v = ½ V~~max~~
- Low Km = high affinity for substrate (less substrate needed)
- High Km = low affinity for substrate

4. ⚗️ Enzyme Concentration [E]

When substrate is in excess, reaction rate is directly proportional to enzyme concentration.
More enzyme molecules = more active sites available = faster product formation.
Clinically, enzyme concentration in blood is measured to diagnose disease (e.g., elevated ALT/AST in liver damage).

5. 🔩 Cofactors and Coenzymes (Activators)

Many enzymes are inactive alone and require non-protein helpers:

Type	Description	Examples
Cofactors	Inorganic metal ions	Zn²⁺, Mg²⁺, Fe²⁺, Cu²⁺
Coenzymes	Small organic molecules (loosely bound)	NAD⁺ (from niacin/Vit B₃), FAD (from riboflavin/Vit B₂)
Prosthetic groups	Coenzymes permanently bound to enzyme	FAD, heme

The complete, active enzyme (protein + cofactor/coenzyme) = Holoenzyme
The inactive protein part alone = Apoenzyme
Most coenzymes are derived from B-vitamins — this is why B-vitamin deficiency causes metabolic disease.

Holoenzyme = Apoenzyme + Cofactor/Coenzyme

6. 🚫 Inhibitors

Any substance that decreases enzyme activity is an inhibitor. (Covered in depth in Question 3.) Key types:

Irreversible — covalent binding (e.g., aspirin, lead)
Reversible — competitive, noncompetitive, uncompetitive

7. 🧂 Ionic Strength / Salt Concentration

High ionic strength decreases enzyme activity by disrupting the ionic interactions that stabilize enzyme structure.
Dilution of clinical samples with appropriate enzyme diluents (containing plasma proteins like albumin) is necessary to maintain accurate enzyme measurements.

8. ⚡ Allosteric Regulation

Small molecules called allosteric effectors bind to a site other than the active site.
They cause conformational changes in the enzyme:
- Allosteric activators → increase activity
- Allosteric inhibitors → decrease activity
This is the main mechanism for feedback regulation in metabolic pathways.

PART 2: NOTE ON PROPERTIES OF ENZYMES

What Are Enzymes?

Enzymes are biological catalysts — they speed up chemical reactions in living organisms without being permanently changed or consumed in the process.

Key Properties

1. Proteins in Nature

All enzymes are proteins (made of amino acids), EXCEPT ribozymes (RNA molecules with catalytic activity — e.g., ribosomes during peptide bond formation).

2. Catalytic Function

Enzymes speed up reactions by lowering the activation energy (Ea) — the energy needed to start the reaction.
They do NOT change the equilibrium of a reaction (the final ratio of products to reactants is unchanged — only the speed of reaching equilibrium changes).

Enzymes lower activation energy — catalyzed vs uncatalyzed reaction

3. High Specificity

Binding specificity: Each enzyme binds only one or a few specific substrates.
Reaction specificity: Each enzyme catalyzes only one type of chemical reaction — virtually no by-products are formed.
Stereospecificity: Enzymes recognize only one mirror-image (enantiomeric) form of a substrate. Example: Proteases act only on L-amino acids (not D-amino acids).

4. Active Site

The active site is a small region on the enzyme where the substrate binds and the reaction occurs.
Two models explain enzyme-substrate binding:
- Lock and Key model: Active site is a rigid, pre-formed shape that perfectly fits the substrate.
- Induced Fit model (more accepted): Active site is flexible; it changes shape when the substrate binds to achieve the best fit.

5. Not Consumed in Reaction

Enzymes are regenerated after each reaction cycle — one enzyme molecule can process thousands of substrate molecules per second.

6. Regulated

Enzyme activity can be turned up or down based on cellular needs via:
- Allosteric regulators
- Covalent modification (e.g., phosphorylation)
- Feedback inhibition (product inhibits early enzyme in a pathway)
- Induction/repression of gene expression

7. Cellular Compartmentalization

Enzymes are localized in specific organelles. Example:
- Krebs cycle enzymes → mitochondria
- Digestive enzymes → lysosomes
- Glycolytic enzymes → cytoplasm
This isolates reactions, prevents interference, and increases efficiency.

8. Cofactor Requirement

Some enzymes need non-protein helpers (cofactors or coenzymes) for activity — without them, they are inactive (apoenzyme form).

9. Enzyme Specificity as Biomarkers

Because many enzymes are tissue-specific, elevated levels in blood indicate organ damage.
- Elevated ALT/AST → liver disease
- Elevated CK-MB → myocardial infarction (heart attack)
- Elevated amylase/lipase → pancreatitis

Summary Table

Property	Key Point
Chemical nature	Proteins (except ribozymes)
Function	Biological catalysts — lower activation energy
Consumed?	No — regenerated after each reaction
Change equilibrium?	No — only speed up reaching it
Specificity	High — one enzyme, one substrate, one reaction
Temperature effect	↑ activity up to optimum → denaturation
pH effect	Optimum pH varies per enzyme
Cofactors	Required by many enzymes; coenzymes often from vitamins
Regulation	Allosteric, covalent modification, feedback inhibition

Sources: Henry's Clinical Diagnosis and Management by Laboratory Methods; Lippincott's Illustrated Reviews: Biochemistry, 8th Ed.

Define enzyme inhibition and discuss the different types of enzymes inhibition. For pharm d 1st year

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Enzyme Inhibition — Definition and Types

Pharm D 1st Year | Biochemistry

DEFINITION

Enzyme inhibition is the process by which a substance (the inhibitor) decreases or completely stops the velocity of an enzyme-catalyzed reaction.

Any substance that can decrease the velocity of an enzyme-catalyzed reaction is considered an inhibitor. Inhibitors are important in biochemistry and pharmacology because at least half of the most commonly prescribed drugs act as enzyme inhibitors.

CLASSIFICATION OF ENZYME INHIBITION

Enzyme Inhibition
├── 1. Irreversible Inhibition
└── 2. Reversible Inhibition
        ├── A. Competitive Inhibition
        ├── B. Noncompetitive Inhibition
        └── C. Uncompetitive Inhibition

1. IRREVERSIBLE INHIBITION

Definition

Irreversible inhibitors bind to the enzyme via covalent bonds, permanently destroying enzyme activity. The inhibition cannot be reversed by dilution or by adding more substrate.

Mechanism

The inhibitor permanently modifies a functional group (e.g., –OH, –SH) at or near the active site.
Once bound, the enzyme molecule is permanently inactive.
The effect is progressive with time — it becomes complete when the amount of inhibitor exceeds the total amount of enzyme.

Key Features

Feature	Detail
Bond type	Covalent (permanent)
Reversible?	No
Effect of adding more substrate	No effect — inhibition is complete
Effect of dilution	No effect
V~~max~~	Permanently decreased

Examples (Pharm D Important)

Inhibitor	Enzyme Inhibited	Clinical Significance
Aspirin	Cyclooxygenase (COX)	Irreversibly inhibits prostaglandin & thromboxane synthesis → anti-inflammatory, antiplatelet
Penicillin / Amoxicillin	Transpeptidase (bacterial cell wall enzyme)	Kills bacteria by blocking cell wall synthesis
Organophosphates (Sarin, Tabun — nerve gases)	Acetylcholinesterase (AChE)	Irreversibly phosphorylates serine in active site → toxic accumulation of acetylcholine
Lead (Pb²⁺)	Ferrochelatase (heme synthesis)	Forms covalent bond with –SH of cysteine → blocks heme synthesis
Methotrexate	Dihydrofolate reductase (DHFR)	Inhibits folate pathway → used in cancer and rheumatoid arthritis

2. REVERSIBLE INHIBITION

Definition

Reversible inhibitors bind to enzymes through non-covalent bonds (ionic interactions, hydrogen bonds, hydrophobic interactions). The inhibitor–enzyme complex can dissociate, and enzyme activity is recoverable by dilution or by adding more substrate.

There are three main types:

A. COMPETITIVE INHIBITION

Definition

The inhibitor is structurally similar to the substrate and competes for the same active site. The enzyme is "deceived" into binding the inhibitor instead of the substrate. Only one can bind at a time.

Mechanism

E + S  ⇌  ES  →  E + P     (normal)
E + I  ⇌  EI  →  no product (inhibited)

The inhibitor binds to the free enzyme only — not the ES complex.

Effects on Kinetics

Parameter	Effect	Reason
V~~max~~	UNCHANGED	Can be overcome by excess substrate
Km	INCREASED (apparent)	More substrate needed to reach ½ V~~max~~

Key rule: Competitive inhibition CAN be overcome by increasing [S].

Lineweaver-Burk Plot (Double Reciprocal Plot)

Lines intersect on the Y-axis (same 1/V~~max~~)
Different X-intercepts (different –1/Km)
Same V~~max~~, different Km

Drug Examples

Drug	Target Enzyme	Use
Statins (atorvastatin, pravastatin)	HMG-CoA reductase	↓ Cholesterol synthesis
Methotrexate	Dihydrofolate reductase	Cancer / autoimmune disease
ACE inhibitors (captopril, enalapril, lisinopril)	Angiotensin-Converting Enzyme	Hypertension
Fluoride ion	Enolase (glycolysis)	Used in lab to prevent glycolysis in blood samples
Malonate	Succinate dehydrogenase (Krebs cycle)	Experimental inhibitor

B. NONCOMPETITIVE INHIBITION

Definition

The inhibitor binds to a different site on the enzyme (allosteric site — NOT the active site). It can bind to both the free enzyme AND the enzyme-substrate (ES) complex, forming an inactive EI or ESI complex. Because it does not compete with the substrate, adding more substrate does NOT help.

Mechanism

E + I  ⇌  EI  →  inactive
ES + I  ⇌  ESI  →  inactive (no product formed)

The inhibitor binds both free enzyme and ES complex, as shown in the diagram below:

Noncompetitive inhibitor binds both free enzyme (EI) and enzyme-substrate complex (ESI)

Effects on Kinetics

Parameter	Effect	Reason
V~~max~~	DECREASED	ESI complex cannot form products; cannot be reversed by adding more substrate
Km	UNCHANGED	Substrate still binds normally to the active site

Key rule: Noncompetitive inhibition CANNOT be overcome by adding more substrate.

Lineweaver-Burk Plot

Lines intersect on the X-axis (same –1/Km)
Different Y-intercepts (different 1/V~~max~~)
Same Km, different V~~max~~

Examples

Inhibitor	Enzyme	Note
Heavy metals (Hg²⁺, Ag⁺)	Various enzymes	Bind –SH groups away from active site
Alanine	Pyruvate kinase	Allosteric feedback inhibition
Cyanide	Cytochrome c oxidase (Complex IV)	Blocks electron transport chain

C. UNCOMPETITIVE INHIBITION

Definition

The inhibitor only binds to the enzyme-substrate (ES) complex — it cannot bind to the free enzyme. It binds at a site that is only exposed after the substrate has bound, forming an inactive ESI ternary complex.

Mechanism

E + S  ⇌  ES        (normal ES complex forms)
ES + I  ⇌  ESI  →   no product (only ESI — dead end)

This is more common in two-substrate reactions (e.g., reactions in lipid or amino acid metabolism).

Effects on Kinetics

Parameter	Effect	Reason
V~~max~~	DECREASED	ESI complex is a dead end
Km	DECREASED	Apparent affinity increases because more ES complex is "trapped" by the inhibitor

Both V~~max~~ and Km decrease proportionally.

Lineweaver-Burk Plot

Lines are PARALLEL (same slope)
Different Y-intercepts
Both V~~max~~ and Km change

Example

Inhibitor	Enzyme
Lithium	Inositol monophosphatase

MASTER COMPARISON TABLE

Feature	Competitive	Noncompetitive	Uncompetitive	Irreversible
Binding site	Active site (same as substrate)	Allosteric site (different)	ES complex only	Active site (covalent)
Binds free enzyme?	Yes	Yes	No	Yes
Binds ES complex?	No	Yes	Yes	—
V~~max~~	Unchanged	Decreased	Decreased	Permanently decreased
Km	Increased	Unchanged	Decreased	—
Overcome by excess [S]?	Yes	No	No	No
Bond type	Non-covalent	Non-covalent	Non-covalent	Covalent
Lineweaver-Burk	Same Y-intercept	Same X-intercept	Parallel lines	—

CLINICAL/PHARMA IMPORTANCE (Must Know for Pharm D)

"At least half of the 10 most commonly prescribed drugs act as enzyme inhibitors." — Lippincott's Illustrated Reviews: Biochemistry

Drug	Type of Inhibition	Enzyme	Effect
Statins	Competitive	HMG-CoA reductase	↓ Cholesterol
Aspirin	Irreversible	COX-1 / COX-2	↓ Inflammation, ↓ platelet aggregation
Penicillin	Irreversible	Transpeptidase	↑ Bacterial death
Captopril / Enalapril	Competitive	ACE	↓ Blood pressure
Methotrexate	Irreversible (tight-binding)	DHFR	Anti-cancer
Organophosphates	Irreversible	Acetylcholinesterase	↑ ACh → toxicity
Allopurinol	Competitive	Xanthine oxidase	↓ Uric acid → treats gout

Sources: Lippincott's Illustrated Reviews: Biochemistry, 8th Ed.; Henry's Clinical Diagnosis and Management by Laboratory Methods; Tietz Textbook of Laboratory Medicine, 7th Ed.; Basic Medical Biochemistry: A Clinical Approach, 6th Ed.

Define enzyme inhibition and discuss the different types of enzymes inhibition

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Enzyme Inhibition — Complete Notes

(Pharm D 1st Year)

DEFINITION

Enzyme inhibition is the process by which a substance called an inhibitor decreases or completely stops the velocity (rate) of an enzyme-catalyzed reaction.

CLASSIFICATION

Enzyme Inhibition
├── 1. Irreversible Inhibition (covalent)
└── 2. Reversible Inhibition (non-covalent)
        ├── A. Competitive
        ├── B. Noncompetitive
        └── C. Uncompetitive

1. IRREVERSIBLE INHIBITION

Inhibitor binds via a covalent bond — permanent, cannot be undone by dilution or adding substrate.
Permanently destroys enzyme function.
Effect is progressive — increases until all enzyme is inactivated.

Drug Examples (High-Yield)

Drug	Enzyme Inhibited	Clinical Use
Aspirin	Cyclooxygenase (COX)	Anti-inflammatory, antiplatelet
Penicillin	Transpeptidase	Antibiotic — kills bacteria
Organophosphates (nerve agents, insecticides)	Acetylcholinesterase	Toxicology
Lead (Pb²⁺)	Ferrochelatase	Blocks heme synthesis (lead poisoning)

2. REVERSIBLE INHIBITION

Inhibitor binds via non-covalent bonds. Enzyme activity can be recovered by dilution or adding more substrate (in some types).

A. COMPETITIVE INHIBITION

Mechanism

Inhibitor is structurally similar to the substrate.
Competes for the same active site as the substrate.
Only one can occupy the active site at a time — substrate and inhibitor cannot bind simultaneously.

E + S  ⇌  ES  →  E + P   (with substrate)
E + I  ⇌  EI  →  no product (with inhibitor)

Kinetic Effects

Parameter	Change	Why
V~~max~~	Unchanged	Excess substrate displaces the inhibitor
Km	Increased	More substrate needed to reach ½ V~~max~~

✅ Can be overcome by increasing substrate concentration

Lineweaver-Burk Plot

Same Y-intercept (same 1/V~~max~~)
Different X-intercepts (different –1/Km)
Lines cross on the Y-axis

Examples

Drug	Enzyme	Use
Statins (atorvastatin)	HMG-CoA reductase	↓ Cholesterol
ACE inhibitors (captopril, enalapril)	Angiotensin-converting enzyme	↓ Blood pressure
Allopurinol	Xanthine oxidase	↓ Uric acid → Gout
Methotrexate	Dihydrofolate reductase (DHFR)	Cancer / autoimmune

B. NONCOMPETITIVE INHIBITION

Mechanism

Inhibitor binds to an allosteric site (different from the active site).
Binds to both free enzyme (E) AND enzyme-substrate complex (ES).
Substrate can still bind to the enzyme, but the reaction cannot proceed normally.
Adding more substrate does NOT help.

E + I  ⇌  EI     → inactive
ES + I ⇌  ESI    → inactive (no product)

Noncompetitive inhibitor binds both free enzyme (EI) and ES complex (ESI)

Kinetic Effects

Parameter	Change	Why
V~~max~~	Decreased	ESI complex is a dead end — cannot form products
Km	Unchanged	Substrate still binds normally

❌ Cannot be overcome by adding more substrate

Lineweaver-Burk Plot

Same X-intercept (same –1/Km)
Different Y-intercepts (different 1/V~~max~~)
Lines cross on the X-axis

Examples

Heavy metals (Hg²⁺, Ag⁺) — bind –SH groups away from active site
Cyanide — inhibits cytochrome c oxidase (Complex IV)
Alanine — noncompetitive inhibitor of pyruvate kinase

C. UNCOMPETITIVE INHIBITION

Mechanism

Inhibitor only binds to the ES complex (not to free enzyme).
The binding site for the inhibitor is only exposed after the substrate binds.
Forms an inactive ESI ternary complex — a dead end.
More common in two-substrate reactions.

E + S  ⇌  ES       (substrate binds first)
ES + I ⇌  ESI  →   no product (dead end)

Kinetic Effects

Parameter	Change	Why
V~~max~~	Decreased	ESI complex cannot yield product
Km	Decreased	More ES complex is trapped → apparent affinity increases

Both V~~max~~ and Km decrease proportionally

Lineweaver-Burk Plot

Parallel lines (same slope)
Different intercepts on both axes
Key identifier: parallel lines = uncompetitive

Example

Lithium — inhibits inositol monophosphatase (used in bipolar disorder treatment)

MASTER COMPARISON TABLE

Feature	Competitive	Noncompetitive	Uncompetitive	Irreversible
Binding site	Active site	Allosteric site	ES complex only	Active site (covalent)
Binds free enzyme?	✅ Yes	✅ Yes	❌ No	✅ Yes
Binds ES complex?	❌ No	✅ Yes	✅ Yes	—
V~~max~~	Unchanged	↓ Decreased	↓ Decreased	↓↓ Permanent
Km	↑ Increased	Unchanged	↓ Decreased	—
Overcome by ↑[S]?	✅ Yes	❌ No	❌ No	❌ No
Bond type	Non-covalent	Non-covalent	Non-covalent	Covalent
Lineweaver-Burk	Same Y-intercept	Same X-intercept	Parallel lines	—

MEMORY TRICKS 🧠

Type	Memory Aid
Competitive	"Compete at the Centre (active site)" — same site, V~~max~~ unchanged
Noncompetitive	"Not at the active site" — different site, Km unchanged
Uncompetitive	"Unwanted guest joins only after the party starts (ES forms first)" — both decrease
Irreversible	"It's permanent — Irreversible like a tattoo"

Sources: Lippincott's Illustrated Reviews: Biochemistry 8th Ed. · Henry's Clinical Diagnosis & Management by Laboratory Methods · Tietz Textbook of Laboratory Medicine 7th Ed.

Define cyclic AMP ? Write the structure and significance the cyclic AMP ?

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