Printed in Great Britain The Nature of Experimental Error in Enzyme Kinetic Measurements

The nature of experimental error in the determination of initial velocities of enzyme-catalysed reactions was investigated. No support was found for the generalization that such velocities should be homogeneous in variance. Instead the variance increased with the velocity in all of the cases studied. The weighting of sets of replicate observations according to their sample variances was tested in simulated experiments and found to give unacceptable results. It was practicable to decide on the best weighting scheme by examin-ing the variability of the deviations from fitted curves, provided that the number of obser-vations was large enough. All procedures for analysing experimental results incorporate some assumptions about the nature of experimental error. But, as Ottaway (1973) has pointed out, there have been no studies in enzyme kinetics to assess what assumptions are appropriate and how far they can be trusted. Consequently, all published discussions of the statistical properties o