Photocatalysis of Fatty Acid Photodecarboxylase (FAP) in Aqueous Solutions and Zeolitic Imidazolate Frameworks (ZIF)

Min-Shih Su 蘇敏仕 )1 , Ya Ting Kao (高雅婷) 1, 2

1 Department of Biological Science and Technology, College of Biological Science and

Technology, National Yang Ming Chiao Tung University

2 Center For Intelligent Drug Systems and Smart Bio devi ces (IDS 2 B)

The light-driven enzyme fatty acid photodecarboxylase (FAP) contains a flavin adenine dinucleotide (FAD) cofactor and harnesses the blue light to drive the decarboxylation on the long-chain fatty acid substrates (C12-C18) and form products of Cn-1alkane/alkene. Under blue light irradiation, a proposed mechanism involves an excited-state electron transfer (ET) from the substrate to the excited-state FAD cofactor. However, an irreversible photoinactivation involving a radical mechanism has been proposed in the absence of substrates.To keep the enzyme stability of cvFAP from photoinactivation, the zeolitic imidazolate frameworks (ZIFs) as cages to shield the denaturation for cvFAP were used. The ZIFs are a metal−organic framework (MOF) formed with zinc ions and organic molecules. The selected cvFAP-ZIF-8 and cvFAP-ZIF-90 bioconjugates with distinct surface properties were used in this study. Here, we used fluorescence-quenching titrations to determine the substrate-binding affinities, the gas chromatography/mass spectroscopy and the fluorometric method to examine the enzyme activity, and the time-correlated single photon counting (TCSPC) to measure the electron transfer (ET) dynamics, in the presence of three substrates. Our results show that FAP performs higher catalytic yield in aqueous solutions, shows lower activity in hydrophilic cvFAP-ZIF-90, and has no activity in hydrophobic cvFAP-ZIF-8. Although the binding affinity decreases with the decrease of the length of the substrate, the ET rates are very similar despite the length of the substrate. Upon forming an enzyme-substrate complex, the FAD cofactor and the carboxyl group of the substrate are in similar proximity regardless of the length of the substrate.