Besides urea, what other compound must be available for the urease enzyme to break down urea?

Answer: Besides urea Other compounds that are available for the break down of urea is Water. It is important for the hydrolysis of urea that results into production of carbon dioxide and ammonia. As ammonia is produced the pH rises and the pH can be maintained by adding acid. The amount of acid added is the measure of rate of hydrolysis.

Urea + Water = Carbon dioxide + Ammonia