Lactate
The reactive form of lactic acid is called lactate. When lactic acid dissociates in physiological conditions, it releases a hydrogen ion (H⁺) and forms its conjugate base, lactate 1.
Chemical Relationship
Lactic acid exists in equilibrium with lactate in biological systems. The key distinction is:
- Lactic acid (CH₃CH(OH)COOH): The protonated form containing a carboxyl group (-COOH)
- Lactate: The deprotonated, anionic form that results when lactic acid loses a hydrogen ion
At physiological pH (~7.4), lactic acid exists predominantly as lactate because the pKa of lactic acid is approximately 3.9. This means that in the body, over 99% exists in the lactate form rather than as lactic acid 1.
Metabolic Context
During anaerobic metabolism and high-intensity exercise, tissue lactate production increases, generating hydrogen ions. The chemical reaction involves bicarbonate buffering:
H⁺ + HCO₃⁻ ↔ H₂CO₃ ↔ CO₂ + H₂O
As lactate production increases [H⁺], this reaction is driven to the right, producing excess CO₂ above that produced aerobically 1.
Important Clinical Distinction
The terms "lactic acid" and "lactate" are often used interchangeably in clinical practice, but technically:
- Lactate is what accumulates in blood and tissues during anaerobic metabolism
- The associated hydrogen ions (not lactic acid itself) contribute to metabolic acidosis
- Clinical measurements report "lactate levels" or "blood lactate," not "lactic acid levels"
This distinction matters because lactate itself is not inherently acidic—it's the accompanying hydrogen ion production during glycolysis that causes acidosis 1.