Evidence for phosphofructokinase in chloroplasts

Abstract

ATTEMPTS to demonstrate phosphofructokinase activity in chloroplasts have so far been unsuccessful^1–4, thus raising the question of whether the transitory starch formed in the chloroplast during photosynthesis can subsequently be metabolised to triose phosphates within the chloroplast. Such a conversion would seem beneficial if the products of starch degradation are required to move freely from the chloroplast to the cytoplasm, since triose phosphates, but not hexose phosphates, are actively and rapidly transported across the chloroplast membrane⁵. The apparent absence of phosphofructokinase from chloroplasts was also discouraging since this enzyme is considered one of the principal regulatory enzymes of carbohydrate metabolism⁶ and the regulatory properties of the plant enzyme have been shown consistent with the control of starch metabolism⁷. Investigations in this laboratory have now demonstrated that chloroplasts do contain phosphofructokinase activity.