Q.Enzymes that catalyse interconversion of optical, geometrical or positional isomers are

Step 1. Recall the six IUBMB enzyme classes. They are grouped by the type of chemical change catalysed: oxidoreductases (redox), transferases (group transfer), hydrolases (hydrolysis), lyases (bond breaking without water), ligases (bond formation using ATP), and isomerases (isomer interconversion).

Step 2. Check option (a) Ligases. Ligases form new bonds using ATP as an energy source (e.g., DNA ligase) - they build new molecules, they do not interconvert isomers.

Step 3. Check option (b) Lyases. Lyases break a chemical bond without adding water - this changes the molecule's composition, it is not an isomer interconversion.

Step 4. Check option (c) Hydrolases. Hydrolases break a bond by adding a water molecule (e.g., digestive enzymes) - again this changes composition, not isomer form.

Step 5. Check option (d) Isomerases. Isomerases specifically catalyse the interconversion of one isomer into another - optical, geometrical (cis-trans) or positional - by internally rearranging atoms within the same molecular formula, exactly matching the question's description.

Match the reaction type described (isomer interconversion) to its IUBMB enzyme class name.

• Confusing isomerase with lyase - lyases break bonds without water but do not specifically interconvert isomers.
• Forgetting that isomerisation does not change the molecular formula, only the arrangement of atoms.