The role of phosphofructokinase in glycolytic control in the facultative anaerobe Sipunculus nudus

The involvement of phosphofructokinase (PFK) in glycolytic control was investigated in the marine peanut worm Sipunculus nudus . Different glycolytic rates prevailed at rest and during functional and environmental anaerobiosis: in active animals glycogen depletion was enhanced by a factor of 120; during hypoxic exposure the glycolytic flux increased only slightly. Determination of the mass action ratio (MAR) revealed PFK as a non-equilibrium enzyme in all three physiological situations. During muscular activity the PFK reaction was shifted towards equilibrium; this might account for the observed increase in glycolytic rate under these conditions. PFK activity, determined under simulated cellular conditions of rest and muscular work, agreed well with the glycolytic flux in the respective situations. However, under hypoxia PFK activity surpassed the glycolytic rate, indicating the PFK may not be rate-limiting under these conditions. The results suggest that glycolytic rate in S. nudus is mainly regulated by PFK during rest and activity. Under hypoxic conditions the regulatory function of PFK is less pronounced.