This question is crucial to my story. I read that cats can't naturally create a specific amino acid, which is why they must eat meat. Are there any other sources a cat-like character could eat?
"Do? I'll tell you what we'll do! We'll be ready!" Matthias, from Redwall
"Life consists of doing the impossible." Brother Fir, The Heir of Mistmantle
I don't think a specific amino acid will be your problem--of all the carnivores, cats need to eat proportionally much more protein and fat than other animals, and very little carbohydrates. They've evolved to eat mostly meat, and do not do well with eating plants. Instead they have devloped many specialized metabolic and digestive processes to adapt to a high percentage of fat and protein in their diets.
Now, I looked it up and I couldn't find any mention of a specific amino acid that they couldn't produce. If, for some reason your character can't eat meat and fish, there might be other sources high in different types of amino acids. For example, legumes and vegetables like spinach, turnips, lettuce, cabbage, beans and some others (just google "foods high in amino acids"). However, I think you'd have a very hard time finding an exact replica of ALL the nutritional needs of a cat. (Or cat-like being). I do think you could come up with some explanation though, if you're willing to stretch your plot a little.
I did find a link on cat diets that you might find useful (I didn't actually read all of it, but here it is anyway):
Gender:
Points: 1509
Reviews: 32