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Next-generation sequencing has resulted in an explosion of available data, much of which remains unstudied in terms of biochemical function; yet, experimental characterization of these sequences has the potential to provide unprecedented insight into the evolution of enzyme activity. One way to make inroads into the experimental study of the voluminous data available is to engage students by integrating teaching and research in a college classroom such that eventually hundreds or thousands of enzymes may be characterized. In this study, we capitalize on this potential to focus on SABATH methyltransferase enzymes that have been shown to methylate the important plant hormone, salicylic acid (SA), to form methyl salicylate. We analyze data from 76 enzymes of flowering plant species in 23 orders and 41 families to investigate how widely conserved substrate preference is for SA methyltransferase orthologs. We find a high degree of conservation of substrate preference for SA over the structurally similar metabolite, benzoic acid, with recent switches that appear to be associated with gene duplication and at least three cases of functional compensation by paralogous enzymes. The presence of Met in active site position 150 is a useful predictor of SA methylation preference in SABATH methyltransferases but enzymes with other residues in the homologous position show the same substrate preference. Although our dense and systematic sampling of SABATH enzymes across angiosperms has revealed novel insights, this is merely the "tip of the iceberg" since thousands of sequences remain uncharacterized in this enzyme family alone., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

The selectivity in the steady state uptakes of Rb(+) and K(+) has been studied in a number of normal and malignant rat tissues. The selectivity is minimal in erythrocytes and the two fastest-growing of four transplantable tumors, in which there is little discrimination between the two ions, and ranges upwards to a maximum Rb(+) uptake in liver. In each tissue, the selectivity is independent of Rb(+) concentration or of K(+) deficiency (except in skeletal muscle). In liver slicesin vitro, reduction of energy metabolism by lowering the temperature or by the addition of metabolic inhibitors reduces the Rb(+)∶K(+) discrimination proportionately much more than K(+) transport. Diaphragm and slices of a transplantable tumor give similar results. With temperature reduction, there is a logarithmic relation between the Rb(+)∶K(+) discrimination ratio and the respiration rate of liver slices. The results are quantitatively accounted for by simultaneous diffusion and metabolically coupled transport across a homogeneous membrane in which Rb(+) transport is more closely coupled than that of K(+) to a metabolic flux across the membrane. There is evidence that the tissue differences in Rb(+)∶K(+) selectivity originate in the different levels of the coupling metabolic flux in different cell types and thus of the energy expenditure on ion transport. In contrast to the differences in steady state selectivity between Rb(+) and K(+), the initial ratio of uptakes of trace(43)K and(86)Rb, in otherwise steady state conditions, is close to unity in both liver and tumor slices, in agreement with theoretical calculations.