The correct answer is Procaine.

Local anesthetics are broadly classified into two categories based on their chemical structure: ester-type and amide-type agents. The key difference between these two classes lies in their metabolism.

- Esther-type local anesthetics, such as Procaine, are primarily metabolized by plasma cholinesterase (also known as pseudocholinesterase), an enzyme found in the blood plasma. This metabolism process occurs quickly, which typically results in a shorter duration of action for ester anesthetics.

- In contrast, amide-type local anesthetics, such as Lidocaine, Prilocaine, and Bupivacaine, are mainly metabolized by the liver through enzymatic degradation by hepatic microsomal enzymes.

This difference in metabolism is clinically important because patients with atypical or deficient plasma cholinesterase may experience prolonged effects or toxicity from ester anesthetics like Procaine.

To summarize:
- Procaine is an ester-type local anesthetic and is metabolized by plasma cholinesterase.
- Lidocaine, Prilocaine, and Bupivacaine are amide-type local anesthetics, metabolized mainly by the liver.

This metabolism difference guides clinical use and helps anticipate potential toxicities.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th Edition, Chapter on Local Anesthetics / Pages 404-410