I’m doing an experiment using competitive and non competitive enzymes on the enzyme B-galactosidase. This enzyme reacts with ONPG and turns yellow, so it can be followed colorimetrically. The non-competitive inhibitor, I2/KI soln, is producing a 0 on the colorimeter. Should it do this or should there be a little enzyme activity?
I’ve tried changing the volumes of enzyme and inhibitor with no result.

Experiment can be found here: http://www.saps.org.uk/attachments/article/95/SAPS%20-%20Inhibitors%20on%20enzyme%20beta-galactosidase%20-%20Scottish%20Highers.pdf