Best assay to determine inhibition

[dhawker]

I need to determine the Ki and IC50 values for a series of compounds with an enzyme I've purified. The problem is that I have to purify the enzyme from whole tissue (pig brain). The yield of the purification is really low, and the process is pretty laborious. I was wondering if anyone could suggest a method to determine these parameters that would use the least amount of enzyme possible. I have access to a 96-well plate reader, so I guess I'm think more along the lines of having to run the minimal number of + combinations as possible to obtain reliable data.