Surface plasmon resonance sensor in the analysis of caffeine binding to CYP1A2 p450 monoxygenase in the presence and absence of NADPH

An alternative to liquid chromatography–mass spectroscopic analysis of CYP catalysis of candidate drugs is proposed by a surface plasmon resonance method. By covalently linking microsomes containing human recombinant CYP1A2, NADPH reductase and cytochrome b5 to a dithiodipropionic acid self-assembly monolayer formed on a gold-coated glass slide, a surface plasmon resonance (SPR) waveguide sensor is investigated. Previously only the CYP monoxygenases have been immobilised for SPR experiments, which bring into question the accuracy of association and dissociation constants determined in the absence of the other essential components (NADPH, NADPH reductase, cytochrome b5) for CYP activity. Caffeine was used as a standard substrate of CYP1A2 and comparisons in the presence and the absence of NADPH were performed to investigate the influence of enabling catalysis upon kinetic constants. This has consequences for future CYP bioassay design as an alternative measure for CYP enzyme kinetics which is demonstrated. The effect of concentration on response time and angular change in the plasmon resonances was also observed, with potential applications for determining metabolism of compounds by this method.