The question of how to distinguish between lipases and esterases is about as old as the definition of the subclassification is. Many different criteria have been proposed to this end, all indicative but not decisive. Here, the activity of lipases in dry organic solvents as a criterion is probed on a minimal α/β hydrolase fold enzyme, the Bacillus subtilis lipase A (BSLA), and compared to Candida antarctica lipase B (CALB), a proven lipase. Both hydrolases show activity in dry solvents and this proves BSLA to be a lipase. Overall, this demonstrates the value of this additional parameter to distinguish between lipases and esterases. Lipases tend to be active in dry organic solvents, while esterases are not active under these circumstances.Catalysts 2020, 10, 308 2 of 17 lipase A (BSLA) [9]. BSLA is a small (181 amino acids, 19 kDa) serine hydrolase ( Figure 1). It is neither interfacially activated nor does it have a lid (criteria one and two) [9,[22][23][24] and sequence data are not conclusive, but it is a minimal α/β hydrolase fold enzyme [9,23,25]. The substrate range clearly qualifies BSLA as a lipase, as does the stability in the presence of solvents [9,[26][27][28][29]. This stability has even been significantly improved in recent mutational studies and BSLA mutants can be very stable in the presence of water-miscible solvents, such as dimethyl sulfoxide (DMSO), dioxane and trifluoroethanol [30,31]. Studies on BSLA in dry organic solvents are, however, missing. As an experimental parameter, we demonstrate the activity of BSLA in dry toluene. Toluene is not water-miscible and has a logP of 2.5 [32]. It is commonly used in organic synthesis and is highly suitable for lipases and also other enzymes with an α/β hydrolase fold. To date, only lipases were shown to be active in toluene with a very low a w [1,3].Catalysts 2019, 9, x FOR PEER REVIEW 2 of 17 interfacially activated nor does it have a lid (criteria one and two) [9,[22][23][24] and sequence data are not conclusive, but it is a minimal α/β hydrolase fold enzyme [9,23,25]. The substrate range clearly qualifies BSLA as a lipase, as does the stability in the presence of solvents [9,[26][27][28][29]. This stability has even been significantly improved in recent mutational studies and BSLA mutants can be very stable in the presence of water-miscible solvents, such as dimethyl sulfoxide (DMSO), dioxane and trifluoroethanol [30,31]. Studies on BSLA in dry organic solvents are, however, missing. As an experimental parameter, we demonstrate the activity of BSLA in dry toluene. Toluene is not watermiscible and has a logP of 2.5 [32]. It is commonly used in organic synthesis and is highly suitable for lipases and also other enzymes with an α/β hydrolase fold. To date, only lipases were shown to be active in toluene with a very low aw [1,3].

Background: The intracellular concentration of heavy-metal cations, such as copper, nickel, and zinc is pivotal for the mycobacterial response to the hostile environment inside macrophages. To date, copper transport mediated by P-type ATPases across the mycobacterial plasma membrane has not been sufficiently explored. Results: In this work, the ATPase activity of the putative Mycobacterium tuberculosis P 1B-type ATPase CtpB was associated with copper (I) transport from mycobacterial cells. Although CtpB heterologously expressed in M. smegmatis induced tolerance to toxic concentrations of Cu 2+ and a metal preference for Cu + , the disruption of ctpB in M. tuberculosis cells did not promote impaired cell growth or heavy-metal accumulation in whole mutant cells in cultures under high doses of copper. In addition, the Cu + ATPase activity of CtpB embedded in the plasma membrane showed features of high affinity/slow turnover ATPases, with enzymatic parameters K M 0.19 ± 0.04 µM and V max 2.29 ± 0.10 nmol/mg min. In contrast, the ctpB gene transcription was activated in cells under culture conditions that mimicked the hostile intraphagosomal environment, such as hypoxia, nitrosative and oxidative stress, but not under high doses of copper. Conclusions: The overall results suggest that M. tuberculosis CtpB is associated with Cu + transport from mycobacterial cells possibly playing a role different from copper detoxification.