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The article focuses on a general acid-base mechanism for the stabilization of a tetrahedral adduct in a serine-carboxyl peptidase. Sedolisins (serine-carboxyl peptidases) belong to a recently characterized family of proteolytic enzymes that have a fold resembling that of subtilisin and a maximal activity at low pH. This family includes the peptidase CLN2, a human enzyme for which mutations in the encoding CLN2 gene lead to a fatal neuro-degenerative disease, that is, classical late-infantile neuronal ceroid lipofuscinosis.

Human activities, such as mining and manufacturing, expose society and the natural environment to harmful levels of metal ions. Recently, optical sensor arrays for metal ion detection have become popular owing to their favourable features, such as facile sample preparation and the requirement of less expensive instrumentation compared to traditional, spectrometry-based analysis techniques. Sensor arrays usually consist of numerous optical probes that are used in combination to generate unique analyte responses. In contrast, here we present an array that comprises a single fluorescent sensor, Coum4-DPA, that produces unique responses to metal ions in different pH environments. With this simple sensing platform, we were able to classify 10 metal ions in different water sources and quantify Pb 2+ in tap water using just one fluorescent sensor, a few pH buffers and two sets of spectral data. This novel approach significantly decreases time and costs associated with probe synthesis and data collection, making it highly transferrable to real-world metal sensing applications., (© 2022 The Authors. Chemistry - An Asian Journal published by Wiley-VCH GmbH.)