The catalytic and regulatory properties of aspartate transcarbamoylase from Pyrococcus abyssi, a new deep-sea hyperthermophilic archaeobacterium

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Abstract
The catalytic and regulatory properties of aspartate transcarbamoylase from Pyrococcus abyssi were studied in the GE5 strain isolated from a deep-sea hydrothermal vent located in the North-Fiji Basin in the SW Pacific Ocean. The enzyme from this hyperthermophilic archaeobacterium shows homotropic cooperative interactions between catalytic sites for the utilization of its two substrates, carbamoylphosphate and aspartate. The activity of this enzyme is subject to allosteric regulation. It is feed-back inhibited by the end-product cytidine triphosphate independently of temperature. In contrast, its sensitivity to the feed-back inhibitor uridine triphosphate and to the activator adenosine triphosphate disappears at high temperature. The unusual response of this aspartate transcarbamoylase to carbamoylphosphate analogues suggests a particular mode of binding of this substrate to the catalytic site as compared to the homologous enzymes of other organisms. Aspartate transcarbamoylase of Pyrococcus abyssi exhibits a remarkable stability towards high temperature and pressure.

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