Enzyme kinetics: partial and complete uncompetitive inhibition

A graphical method for analysing enzyme data to obtain kinetic parameters, to identify the types of inhibition and the enzyme mechanisms is described. The method consists of plotting experimental data as v/(V₀−v) versus 1/(I) at different substrate concentrations. I is the inhibitor concentration; V₀ and v are the initial rates of enzyme reaction attained by the system in the presence of a fixed amount of substrate and in the absence and presence of inhibitor respectively. Complete inhibition gives straight lines that pass through the origin while partial inhibition gives straight lines that converge on the 1/I-axis at a point away from the origin. With uncompetitive inhibition the slopes of the lines decrease with increasing substrate concentration. The kinetic parameters K_m, K′_i and β (degree of partiality) can best be determined from respective secondary plots of slope and intercept versus reciprocal of substrate concentration.