Characterisation of kinetics, substrate inhibition and product activation by AMP of bifunctional ADP‐dependent glucokinase/phosphofructokinase from Methanococcus maripaludis

Methanogenic archaea have received attention due to their potential use in biotechnological applications such as methane production, so their metabolism and regulation are topics of special interest. When growing in a nutrient‐rich medium, these organisms exhibit gluconeogenic metabolism; however, under starvation conditions, they turn to glycolytic metabolism. To date, no regulatory mechanism has been described for this gluconeogenic/glycolytic metabolic switch. Here, we report that adenosine monophosphate (AMP) activates both enzymatic activities of the bifunctional adenosine diphosphate (ADP)‐dependent phosphofructokinase/glucokinase from Methanococcus maripaludis (MmPFK/GK). To understand this phenomenon, we performed a comprehensive kinetic characterisation, including determination of the kinetics, substrate inhibition and AMP activation mechanism of this enzyme. We determined that MmPFK/GK has an ordered‐sequential mechanism, in which MgADP is the first substrate to bind and AMP is the last product released. The enzyme also displays substrate inhibition by both sugar substrates; we determined that this inhibition occurs through the formation of catalytically nonproductive enzyme complexes caused by sugar binding. For both activities, the AMP activation mechanism occurs primarily through incremental changes in the affinity for the sugar substrate, with this effect being higher in the GK than in the PFK activity. Interestingly, due to the increase in the sugar substrate affinity caused by AMP, an enhancement in the sugar substrate inhibition effect was also observed for both activities, which can be explained by an increase in sugar binding leading to the formation of dead‐end complexes. These results shed light on the regulatory mechanisms of methanogenic archaeal sugar metabolism, a phenomenon that has been largely unexplored. Regulatory mechanisms of methanogenic archaeal enzymes are largely unexplored. Here, we report that both enzymatic activities of the bifunctional ADP‐dependent phosphofructokinase/glucokinase from M. maripaludis are activated by AMP, a product of the catalysed reaction, mainly by an increase in sugar binding affinity. This step could represent a metabolic switch for methanogenic organisms when under starvation glycolysis must be activated to degrade glycogen stores.