Azurin and HS–: Towards Implementation of a Sensor for HS– Detection

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Hydrogen sulfide (H 2 S) is an important biological messenger, which recently joined nitric oxide (NO) and carbon monoxide (CO) as an endogenously produced gasotransmitter. This discovery resulted in a renewed interest towards H 2 S and, in particular, in its reactivity with biological and bioinorganic targets. However, in the scientific literature studies exploring the reactivity of H 2 S/HS – with non‐heme proteins are rare. In this work, we studied the interaction of HS – with the natural metalloprotein Cu‐azurin and its cobalt variant via UV‐Vis, fluorescence, and EPR spectroscopy, as well as X‐ray diffraction. Interaction of HS – significantly enhances the fluorescence emission of fluorescently labelled copper azurin in buffered solutions and at physiological pH. In contrast, fluorescently labelled cobalt azurin undergoes a fluorescence quenching in the presence of HS – in line with the changes observed in the absorption spectrum of the construct. The results highlight the potential of azurin for implementation in a fast and simple HS – sensor.