The lock-and-key mechanism refers to

The Correct Answer is:

Emil Fischer was the first to describe the Lock-and-Key mechanism, which involves an enzyme momentarily binding to one substrate to generate a substrate complex.

Complementary enzyme forms that share a single substrate are usually linked with the locking mechanism and key, with the enzyme acting as the lock and the substrate acting as the key. One substrate (key) fits perfectly in the active site (keyhole) of the enzyme (lock).

The substrate and the above-mentioned active site are physically compatible. This is the transient binding site for enzymes. The enzyme is supposed to fit the lock and the substrate together like a lock and a key.