A mixed hard- and soft-modelling approach to study and monitor enzymatic systems in biological fluids

Abstract Mixed hard- and soft-modelling multivariate curve resolution (HS-MCR) is applied to study and to monitor complex enzymatic systems. Working under the basis of the soft-modelling technique multivariate curve resolution-alternating least squares (MCR-ALS), a hard constraint is introduced to force some or all concentration profiles to fulfil an enzymatic model. In this way, improvements to the application of pure hard- or pure soft-modelling are achieved. The enzymatic reactions of different mixtures of hypoxanthine, xanthine and uric acid with xanthine oxidase are studied. This is a complex enzymatic process, where uric acid acts as a linear competitive inhibitor. The reactions were monitored with UV–vis spectrophotometry coupled to a stopped-flow module. This work has two aims, both of them focusing on different aspects linked to modelling enzymatic systems using HS-MCR. The first goal is related to the elucidation of the real enzymatic mechanism when one of the chemical substances involved in the process apparently deviates from the mechanism found in the literature. The second one focuses on modelling the enzymatic reaction in the presence of a biological interference, such as human urine. The elucidation of the real mechanism of this enzymatic process and of the behaviour of the involved chemical species in a natural absorbing medium are good examples of situations that can benefit from mixed modelling approaches involving the best of hard- and soft-modelling methodologies.