Exploring the Increased Activity of the Blue Light-Dependent Photoenzyme Fatty Acid Photodecarboxylase under Violet Light

Fatty acid photodecarboxylase (FAP) is a FAD-containing enzyme that catalyzes the light-driven decarboxylation of medium-long chain fatty acids. Over recent years, the substrate scope of FAP has been broadened to improve its potential to catalyze a range of blue light-dependent industrially relevant reactions. However, photoinactivation constitutes a major hurdle for generalized applications. Previous studies have suggested that violet light may be a more suitable illumination wavelength for many of these applications. Here, we have investigated any possible enhancement in the catalytic activity of FAP upon illumination with violet light and utilized a spectrophotometric assay that detects the production of CO₂ in real time to monitor the FAP reaction under different illumination conditions. We show that the activity of FAP at low intensities of violet light is approximately 6-fold higher than under identical illumination conditions with blue light. Moreover, the product yield increases further when the light is delivered in a pulsed manner, most likely as a result of lower levels of photoinactivation than is observed upon continuous illumination. More detailed spectrophotometric measurements have confirmed that FAP employs a similar catalytic cycle upon illumination with both violet and blue light. Rather, the enhancement in catalytic efficiency observed with violet light is attributable to higher populations of excited state FAD species that can proceed along a productive catalytic pathway. We suggest that pulses of low-intensity violet light provide an optimized route for FAP catalysis, highlighting the importance of illumination conditions in the expanding field of flavin-based photobiocatalysis.