This enzyme was first isolated and purified in the form of crystals

The correct option is Urease.

Step-by-Step Explanation:

1. Historical Context: In the early 20th century, the chemical nature of enzymes was highly debated. Many scientists believed that enzymes were not proteins but rather some other class of chemical compounds or carriers.

2. The Breakthrough: In 1926, the American biochemist James B. Sumner succeeded in isolating and crystallizing the enzyme urease from the jack bean (Canavalia ensiformis).

3. Significance: Sumner's crystallization of urease provided the first definitive chemical proof that enzymes are proteins. He demonstrated that the crystals consisted entirely of protein, and when dissolved, they retained their enzymatic activity. For this pioneering work, Sumner was awarded the Nobel Prize in Chemistry in 1946.

4. Other Options:
- Pepsin was crystallized later, in 1930, by John H. Northrop.
- Amylase and Ribonuclease were also crystallized subsequently as the techniques for protein purification advanced.
Therefore, urease remains historically significant as the very first enzyme to be isolated and purified in crystalline form.