Carbonic Anhydrase
கார்போனிக் அன்ஹைட்ரேஸ்
Without Carbonic Anhydrase, your blood would be a CO2-saturated death trap. This enzyme is the fastest catalyst in your body, operating at a rate of 600,000 reactions per second. If you think respiration is just about lungs, you are failing the basics of gas transport.
The idea
Carbonic Anhydrase is a zinc-containing enzyme found in high concentration within RBCs and in minute quantities in blood plasma. It catalyzes the reversible reaction: CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+. This reaction is crucial for the transport of CO2 from tissues to the lungs as bicarbonate ions.
Why it matters
It accelerates the conversion of CO2 into bicarbonate, which is the primary method of CO2 transport in the blood.
NEET lens
NEET focuses on the enzyme's location and the reaction direction. Remember: high concentration in RBCs, low in plasma. Do not confuse the direction of the reaction at the tissues versus the alveoli. Expect questions on the specific ions involved in the equilibrium.
Clinical significance
Inhibition of this enzyme leads to metabolic acidosis, as the body fails to regulate blood pH through bicarbonate buffering. Acetazolamide, a drug used for altitude sickness, works by inhibiting this enzyme to alter renal bicarbonate excretion. When this system fails, the body's acid-base homeostasis collapses instantly.
Introduction
Carbonic anhydrase (CA) is a zinc-containing enzyme in red blood cells that catalyzes the rapid interconversion between CO₂ and carbonic acid (H₂CO₃), enabling efficient CO₂ transport in blood.
Core concept
Reaction: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻. In tissues (CO₂ produced): CO₂ enters RBCs → CA catalyzes CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻. HCO₃⁻ exits to plasma (chloride shift: Cl⁻ enters). H⁺ buffered by Hb → reduced O₂ affinity (Bohr effect). In lungs (CO₂ released): HCO₃⁻ enters RBCs → CA reverses: HCO₃⁻ + H⁺ → H₂CO₃ → CO₂ + H₂O → CO₂ exhaled. CA speeds up this reaction 10 million-fold (uncatalyzed reaction too slow for physiological timescales).
Go deeper
CO₂ transport forms: ~70% as HCO₃⁻ in plasma (after CA action in RBCs). ~23% as carbaminohemoglobin (CO₂ bound to Hb amino groups). ~7% dissolved in plasma. Most CO₂ travels as HCO₃⁻ — enabled entirely by carbonic anhydrase. Without CA, CO₂ transport would be catastrophically insufficient.
From Class 10
CO₂ from respiration must be transported to the lungs and exhaled. The enzyme carbonic anhydrase makes this possible by rapidly converting CO₂ to a water-soluble form in blood.