An enzyme has a KM of 20 µM and a Vmax of 50 mmoles/minute/µg. After exposure to an inhibitor and analysis on a Lineweaver - Burk plot the following values are obtained: -1/KM = - 0.05 liters/µmole and 1/Vmax = 0.04 (mmoles of product/minute/µg of enzyme)-1. What kind of inhibitor was used in the experiment?