Please, as I asked earlier, tell us what you get and what you expect to get. I ran this simplified version of your code
f = @(x,a0,a1) (a0.*x)./(a1+x);
The displayed answer is 0.3333. This is the answer I would expect to get.
I am trying to understand what you think would be different. One possibility is that you are getting confused about variable values that are defined before you define the function, which may be irrelevant because the function arguments will be used instead.