Tyrosinase is a copper enzyme with broad substrate specifity toward a lot of phenols with different biotechnological applications. The availability of quick and reliable measurement methods of the enzymatic activity of tyrosinase is of outstanding interest. A series of spectrophotometric methods for determining the monophenolase and diphenolase activities of tyrosinase are discussed. The product of both reactions is the o-quinone of the corresponding monophenol/diphenol. According to the stability and properties of the o-quinone, the substrate is classified as four substrate types. For each of these substrate types, we indicate the best method for measuring diphenolase activity (among eight methods) and, when applicable, for measuring monophenolase activity (among four methods). The analytical and numerical solutions to the system of differential equations corresponding to the reaction mechanism of each case confirm the underlying validity of the different spectrophotometric methods proposed for the kinetic characterization of tyrosinase in its action on different substrates.

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The COVID-19 pandemic made clear how our society requires quickly available tools to address emerging healthcare issues. Diagnostic assays and devices are used every day to screen for COVID-19 positive patients, with the aim to decide the appropriate treatment and containment measures. In this context, we would have expected to see the use of the most recent diagnostic technologies worldwide, including the advanced ones such as nano-biosensors capable to provide faster, more sensitive, cheaper, and high-throughput results than the standard polymerase chain reaction and lateral flow assays. Here we discuss why that has not been the case and why all the exciting diagnostic strategies published on a daily basis in peer-reviewed journals are not yet successful in reaching the market and being implemented in the clinical practice.

We show that the conformational features of the molecular complexes of E. coli beta-galactosidase and O-glycosides may differ from those formed with closely related compounds in their chemical nature, such as C- and S-glycosyl analogues. In the particular case presented here, NMR and ab initio quantum mechanical results show that the 3D-shapes of the ligand/inhibitor within the enzyme binding site depend on the chemical nature of the compounds. In fact, they depend on the relative size of the stereoelectronic barriers for chair deformation or for rotation around Phi glycosidic linkage.

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dec-cis-9-enoic acid) is a hydroxylate fatty acid which has many industrial uses (Bonjean, 1991;Brigham, 1993). It Castor (Ricinus communis L.) oil is characterized by high levels has been identified as a constituent of the seed storage of ricinoleic acid content (about 900 g kg Ϫ1 ) and low levels of oleic oil in at least 12 genera of higher plants (van de Loo et acid (about 30 g kg Ϫ1 ). A total of 191 accessions of a germplasm collection of castor were evaluated for oil content and fatty acid al., 1993), such as Linum (Linaceae) (Green, 1984), and composition of the seed oil with an attempt to widen the variability Lesquerella (Brassicaceae) (Broun et al., 1998). Current for these traits in this species. As a result of this evaluation, the knowledge on fatty acid biosynthesis in castor indicates natural mutant line OLE-1 with approximately 780 g kg Ϫ1 of oleic