Glycolysis during gluconeogenesis in cotyledons of Cucurbita pepo

Abstract

The aim of this work was to investigate the extent of glycolysis during gluconeogenesis in the germination of marrow ( Cucurbita pepo L. var. medullosa Alef.). The activities of phosphofructokinase (E.C. 2.7.1.11) in extracts of cotyledons, of seeds, and seedlings grown in the dark for 2, 5, and 8 days were 3·5, 4·8, 9·4, and 11·8 nmol substrate consumed per cotyledon per min, respectively. The comparable figures for pyruvate kinase (E.C. 2.7.1.41) were 16·3, 72·3, 974, and 1485. The patterns of 14CO 2 production from [1- 14C], [2- 14C], [3,4- 14C], and [6- 14C]glucose indicated that at all the above stages of germination glycolysis was appreciable and predominated over the pentose phosphate pathway. These patterns, and the distribution of label from [1- 14C], and [3- 14C]pyruvate supplied to 5-day-old cotyledons, indicated that the pyruvate formed in glycolysis was converted to acetyl units that were used primarily in biosyntheses. It is concluded that glycolysis occurred at all the stages of germination examined and was particularly active during gluconeogenesis. It is suggested that the significance of this glycolysis is the provision of intermediates for biosyntheses, a need that may not be met by corresponding gluconeogenic intermediates as these may be retained within organelles.