Gluconeogenesis in the Castor Bean Endosperm

Abstract

The control points of the Embden-Meyerhof-Parnas path-way in germinating castor bean (Ricinus communis) endo-sperms are sought in two ways: (a) by measuring the amounts of various glycolytic intermediates at intervals during the germination; (b) by determining the crossover points appearing during anoxia. A significant departure from thermodynamic equilibrium between substrates and products is found at the level of fruc-tose 1,6-diphosphatase and phosphofructokinase. A definite shift of this ratio is observed at the onset of active gluconeo-genesis. The concentrations of phosphoenolpyruvate and 3-phosphoglyceric acid increase at the same time. Another departure from the expected equilibrium is also observed at the level of the pyruvate kinase. The imposition of anoxia on 3-day-old endosperms reveals two crossover points, at the level of the same enzymes. It is therefore concluded that they regulate the glycolytic flow.