I am not 100% sure whether it's acceptable or not so I will not comment on it but one thing I know is that some schools will specifically require for LORs from certain classes' professors (bio, chem, etc.) and if you are submitting TAs LOR, it would not work for them (and many times school will not tell you that you're not even considered for interview because your application is not complete until you call them)
Make sure to at least look at all the schools you're planning on applying and their requirements for LORs.
It is always the safest to go with professors (and science professors) since that would work out with most of school's requirements.