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A new crystallographic structure of the free active‐site R conformer of the allosteric enzyme glucosamine‐6‐phosphate deaminase from Escherichia coli, coupled with previously reported structures of the T and R conformers, generates a detailed description of the heterotropic allosteric transition in which structural flexibility plays a central role. The T conformer's external zone [Horjales et al. (1999), Structure, 7, 527–536] presents higher B values than in the R conformers. The ligand‐free enzyme (T conformer) undergoes an allosteric transition to the free active‐site R conformer upon binding of the allosteric activator. This structure shows three alternate conformations of the mobile section of the active‐site lid (residues 163–182), in comparison to the high B values for the unique conformation of the T conformer. One of these alternate R conformations corresponds to the active‐site lid found when the substrate is bound. The disorder associated with the three alternate conformations can be related to the biological regulation of the Km of the enzyme for the reaction, which is metabolically required to maintain adequate concentrations of the activator, which holds the enzyme in its R state. Seven alternate conformations for the active‐site lid and three for the C‐terminus were refined for the T structure using isotropic B factors. Some of these conformers approach that of the R conformer in geometry. Furthermore, the direction of the atomic vibrations obtained with anisotropic B refinement supports the hypothesis of an oscillating rather than a tense T state. The concerted character of the allosteric transition is also analysed in view of the apparent dynamics of the conformers.

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Wastewater treatment and simultaneous production of value-added products with microalgae represent a sustainable alternative. Industrial wastewater, characterized by high C/N molar ratios, can naturally improve the carbohydrate content in microalgae without the need for any external source of carbon while degrading the organic matter, macro-nutrients, and micro-nutrients. This study aimed to understand the treatment, reuse, and valorization mechanisms of real cooling tower wastewater (CWW) from a cement-processing industry mixed with domestic wastewater (DW) to produce microalgal biomass with potential for synthesis of biofuels or other value-added products. For this purpose, three photobioreactors with different hydraulic retention times (HRT) were inoculated simultaneously using the CWW-DW mixture. Macro- and micro-nutrient consumption and accumulation, organic matter removal, algae growth, and carbohydrate content were monitored for 55 days. High COD (> 80%) and macronutrient removals (> 80% of N and P) were achieved in all the photoreactors, with heavy metals below the limits established by local standards. The best results showed maximum algal growth of 1.02 g SSV L−1 and 54% carbohydrate accumulation with a C/N ratio of 31.24 mol mol−1. Additionally, the harvested biomass presented a high Ca and Si content, ranging from 11 to 26% and 2 to 4%, respectively. Remarkably, big flocs were produced during microalgae growth, which enhanced natural settling for easy biomass harvesting. Overall, this process represents a sustainable alternative for CWW treatment and valorization, as well as a green tool for generating carbohydrate-rich biomass with the potential to produce biofuels and fertilizers.

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