Enzyme nomenclature — lactic acid stereochemistry: Which enzyme converts optically active L- or D-lactic acid into an optically inactive racemic mixture (DL-lactic acid)?

Introduction / Context:
Optical activity matters in bioprocessing and product functionality. Enzymes that interconvert stereoisomers play key roles in value-added transformations and analytical preparations.

Given Data / Assumptions:

• Lactic acid exists as D- and L- forms.
• The task is to convert a single enantiomer into a racemic mixture.
• We must match the correct enzyme class.

Concept / Approach:
A racemase catalyzes the interconversion of enantiomers at a single stereogenic center, yielding racemic products from optically pure substrates. While isomerases convert between structural or geometric isomers, racemases are the specific subclass for chiral center inversion. Dehydrogenases catalyze redox reactions; invertase hydrolyzes sucrose to glucose and fructose.

Step-by-Step Solution:
Identify the need: D ↔ L interconversion at one chiral center.Map this to the enzyme class: racemase.Exclude enzymes with unrelated catalytic functions (redox, hydrolysis).

Verification / Alternative check:
Biochemistry texts classify alanine racemase and lactate racemase as prototypical racemases acting on amino acids or hydroxy acids.

Why Other Options Are Wrong:

• Isomerase: Too broad; racemase is the precise subclass.
• Dehydrogenase/Invertase/Hydratase: Catalyze different reaction types.

Common Pitfalls:
Using “isomerase” generically when a specific stereochemical term (racemase) is warranted.

Final Answer:
racemase.