Distinguish competitive and non-competitive inhibition

2.5.11 · Biology › Enzymes & Bioenergetics Basics

Hum care kyun karte hain?

Enzymes reactions ko speed up karte hain. Inhibitors unhe slow karte hain — aur kaise ek drug ya poison enzyme ko slow karta hai, yeh batata hai ki woh kahan bind karta hai aur usse kaise haraayein. Agar doctor jaanta hai ki inhibitor competitive hai, toh woh samajhta hai ki "zyada substrate se fix ho jaayega." Agar non-competitive hai, toh "zyada substrate bekaar hai." Yeh ek distinction poori treatment logic badal deti hai. Yeh 80/20 core hai: do binding stories → do kinetic signatures.

HAR cheez KYA hai

Kinetics kaise nikalta hai (derive karo, memorise mat karo)

Michaelis–Menten se shuru karo. Reaction: $E + S ⇌ E S \to E + P$

Steady-state use karte hue, rate hai: $v = \frac{V _{ma x} [ S ]}{K _{m} + [ S ]}$

Yeh form kyun? $v$ , $[S]$ ke saath badhti hai lekin plateau karta hai kyunki enzyme molecules sirf itne hi hain. Jab $[S] = K_{m}$ , plug in karo: $v = V_{ma x} \cdot K_{m} / (K_{m} + K_{m}) = V_{ma x} /2$ . ✔ Isliye $K_{m}$ half-max concentration hai.

Competitive case — effect derive karo

Inhibitor free enzyme chura leta hai: $E + I ⇌ E I$ . Yeh free $E$ ko remove karta hai, toh enzyme lagta hai substrate ko worse bind karta hai. Define karo $α = 1 + [I] / K_{i}$ . Math se milta hai: $v = \frac{V _{ma x} [ S ]}{α K _{m} + [ S ]}$

Yeh step kyun? Inhibitor tabhi compete karta hai jab free enzyme ho. Bahut zyada $[S]$ daalo aur substrate race jeet jaata hai — toh $v \to V_{ma x}$ phir bhi hota hai. Lekin apparent $K_{m}$ ban jaata hai $α K_{m}$ (bada → lagta hai affinity kam hai).

$V_{ma x} unchanged, K_{m} increases$

Non-competitive case — effect derive karo

Inhibitor reversibly $E$ aur $E S$ dono pe equally bind karta hai (alag site pe). Kisi bhi moment pe enzyme ka ek fraction inhibitor-bound, non-functional form mein hota hai — lekin kyunki binding reversible hai, yeh ek dynamic equilibrium hai, permanent removal nahin. $α^{'} = 1 + [I] / K_{i}$ ke saath: $v = \frac{( V _{ma x} / α ^{'} ) [ S ]}{K _{m} + [ S ]}$

Yeh step kyun? Kisi bhi moment pe enzyme ka ek fraction substrate ke baad bhi inactive hota hai, toh substrate flood karna rescue nahin kar sakta → $V_{ma x}$ drops. Lekin jo substrate bind karta hai woh same affinity se bind karta hai → $K_{m}$ unchanged.

$V_{ma x} decreases, K_{m} unchanged$

Figure — Distinguish competitive and non-competitive inhibition

Worked examples

Worked example Example 2 — Ek reversible allosteric inhibitor

Maan lo ek small molecule ek enzyme ke allosteric site pe reversibly bind karta hai (jaise kuch reversible product-like effectors), active site ko distort karta hai bina substrate se resemblance ke, aur freely dissociate hota hai. Step: Active site? Nahin, allosteric hai, aur reversible → non-competitive. Kyun? Yeh active site se door bind karta hai, toh substrate daalke ise hataya nahin ja sakta, phir bhi kyunki yeh dissociate hota hai enzyme kabhi permanently destroy nahin hoti. Prediction: $V_{ma x}$ ↓, $K_{m}$ same. Contrast (YEH category NAHIN hai): Pb²⁺ ya doosre heavy metals jo cysteine –SH groups se bind karte hain woh usually irreversibly bind karte hain, toh woh irreversible inhibitors hain, pure reversible non-competitive nahin — unhe upar wale $V_{ma x}$ / $K_{m}$ pattern se analyse mat karo.

Common mistake Galat ideas ko steel-man karo

Galat idea A: "Competitive inhibitors $V_{ma x}$ kam karte hain kyunki woh enzyme block karte hain." Kyun sahi lagta hai: blocking se lagta hai max drop hona chahiye. Fix: block temporary aur reversible hai; system mein substrate flood karo aur substrate har collision jeet jaata hai, toh ceiling $V_{ma x}$ phir bhi reach ho jaata hai — bas zyada $[S]$ lagta hai. Penalty $K_{m}$ mein dikhta hai, $V_{ma x}$ mein nahin.

Galat idea B: "Non-competitive inhibitors ko substrate jaisa hona chahiye." Kyun sahi lagta hai: hum assume karte hain inhibition matlab same spot ke liye compete karna. Fix: non-competitive inhibitors ek alag (allosteric) site pe bind karte hain, toh unhe koi structural resemblance ki zaroorat nahin.

Galat idea C: "Zyada substrate hamesha inhibition reverse kar deta hai." Kyun sahi lagta hai: competitive ke liye kaam karta hai, toh hum generalise karte hain. Fix: non-competitive ke liye yeh kuch nahi karta — kisi bhi moment pe enzyme ka ek hissa inactive hota hai substrate ke baad bhi.

Galat idea D: "Non-competitive inhibition matlab enzyme permanently knock out ho gayi." Kyun sahi lagta hai: ghata hua $V_{ma x}$ lagta hai jaise enzyme destroy ho gayi hai. Fix: classic non-competitive inhibition reversible hai — inhibitor bind aur release karta hai ek dynamic equilibrium mein; permanent destruction irreversible inhibitors define karta hai.

Recall Feynman: ek 12-saal ke bacche ko samjhao

Socho ek keyhole (enzyme) aur sahi key (substrate). Ek competitive cheater ek fake key lekar ata hai aur keyhole jam karta hai — lekin agar tum hazar asli keys laao, ek toh eventually andar aa jaayegi. Ek non-competitive cheater door frame ko pakad ke thodi der ke liye moda deta hai, toh asli key bhi theek se nahin ghoomti — lekin yeh cheater chodta rehta hai aur phir pakadta hai (reversible), yeh door kabhi permanently nahin todta. Kitni bhi asli keys laao, ek moda hua frame theek nahin hoga.

Flashcards

Competitive inhibitor kahan bind karta hai?

Active site pe (substrate ke same site pe).

Non-competitive inhibitor kahan bind karta hai?

Ek alag, allosteric site pe (reversibly).

Competitive inhibition ka

V_{ma x}

aur

K_{m}

pe kya effect hai?

V_{ma x}

unchanged,

K_{m}

increases.

Non-competitive inhibition ka

V_{ma x}

aur

K_{m}

pe kya effect hai?

V_{ma x}

decreases,

K_{m}

unchanged.

Kaun si inhibition zyada substrate daalke reverse hoti hai?

Competitive.

Competitive mein

V_{ma x}

unchanged kyun rehta hai?

Excess substrate inhibitor ko out-compete karta hai, toh saturation abhi bhi full rate tak pahuncha hai.

Non-competitive

V_{ma x}

kyun lower karta hai?

Kisi bhi moment pe enzyme ka ek fraction inactive hota hai substrate ke baad bhi; substrate flood karna ise rescue nahin kar sakta.

Kya classic non-competitive inhibition reversible hai?

Haan — yeh allosteric site pe reversible binding hai (permanent knockout = irreversible inhibition).

Lineweaver–Burk pe competitive lines kaun se axis pe intersect karti hain?

Y-axis pe (same

1/ V_{ma x}

Lineweaver–Burk pe non-competitive lines kaun se axis pe intersect karti hain?

X-axis pe (same

- 1/ K_{m}

Kya non-competitive inhibitor substrate se milta hai?

Zaroor nahin; yeh kahin aur bind karta hai.

Low

K_{m}

kya indicate karta hai?

High substrate affinity.

Cysteine –SH groups se bind karne waale heavy metals usually kaun se inhibitor hote hain?

Irreversible inhibitors (pure reversible non-competitive nahin).

Dono effects ka mnemonic?

"Com-K, Non-V": Competitive→Kₘ, Non-competitive→Vₘₐₓ.

Connections

Michaelis-Menten Kinetics
Km and Vmax meaning
Lineweaver-Burk Plot
Allosteric Regulation
Enzyme Active Site & Induced Fit
Drug Design and Enzyme Inhibitors
Uncompetitive Inhibition
Irreversible Inhibition