The conversion of urea to ammonia depends on urease, an enzyme. how would the conversation be affected if the body could not make urease

   The answer here is quite different, an enzyme is always going to be specific, so for example, cows, they have inside their digestive system an enzyme to digest cellulose, if they didn't have this, it would cause several problems.

   In this case, if the conversion doesn't happen, the conversation wasn't going to happen too, and then the body would start to feel the symptoms, as well as your kidney, you'd put a lot of pressure on him to filter out all this urea that wasn't supposed to be there, and that could cause problems like urinary stones or infections that could lead you even to ulcers.