Transaminases (TA) which offer a highly stereoselective access to chiral amino pharmaceuticals and bioactive compounds have gained considerable attention in the past few years.1–3 The availability of efficient screening assays is of high importance to detect, in wild type or mutant enzymes libraries, the wanted TA for a specific application. Therefore, in the course of our research aimed at the design of new TA-catalysed processes,4–6 we have developed a new screening method for amine-TA. This method is based on the use of hypotaurine (HPT) as amino donor substrate, which is converted upon transamination into 2-oxoethylsulfinic acid, itself instantaneously decomposed into sulfite and acetaldehyde. Sulfite ions can then be easily detected by spectrophotometry at 412 nm using Ellman’s reagent, thus allowing direct kinetic measurements. As shown below, two complementary assays were developed based on this titration method. The direct assay allows to detect a HPT-TA, ie an enzyme active with any chosen acceptor and HPT as donor. These HPT-TA catalyse an irreversible transamination, provided that they don’t accept acetaldehyde as substrate. In the coupled assay, L- or D-Ala is used as generic donor substrate of amine-TA and is regenerated using an auxiliary HPT-TA. This coupled reaction thus allows the activity measurement and can afford an equilibrium shift. We will present the development and application of this method for the screening of a collection of 375 Amine-TA from biodiversity. The direct assay implementation allowed to identify several highly active HPT-TA, whereas the enzyme with the most restricted substrate spectrum proved suitable for use as the auxiliary enzyme in the coupled assay. This latter general screening assay was then successfully employed for the activity assessment of diverse amine-TA with Ala and a variety of acceptor substrates. References: 1 D. Patil, M.; Grogan, G.; Bommarius, A.; Yun, H.; D. Patil, M.; Grogan, G.; Bommarius, A.; Yun, H. (2018), Catalysts, 8: 254. 2 Gomm, A.; O’Reilly, E. (2018), Curr. Opin. Chem. Biol., 43: 106–112. 3 Ferrandi, E. E.; Monti, D. (2017), World J Microbiol Biotechnol., 34:13. 4 Guérard-Hélaine, C.; Heuson, E.; Ndiaye, M.; Gourbeyre, L.; Lemaire, M.; Hélaine, V.; Charmantray, F.; Petit, J.-L.; Salanoubat, M.; Berardinis, V. de; et al. (2017), Chem. Commun., 53: 5465–5468. 5 Heuson, E.; Petit, J.-L.; Debard, A.; Job, A.; Charmantray, F.; Berardinis, V. de; Gefflaut, T. (2015), Appl Microbiol Biotechnol, 100: 397–408. 6 Heuson, E.; Charmantray, F.; Petit, J.-L.; de Berardinis, V.; Gefflaut, T. (2019), Advanced Synthesis & Catalysis, 361: 778–785.