It was in 1909 that Young, in the laboratory of Harden, isolated from fermenting yeast the fructose bisphosphate (the Harden and Young ester) that was later identified by Levene & Raymond (1928) as fructose 1,6-bisphosphate. Some 71 years elapsed until a second fructose bisphosphate was isolated from living cells and identified as fructose 2,6bisphosphate (Van Schaftingen et al., 1980c). In contrast with its elder brother, Fru-2,6-P2 is not an intermediary metabolite of glycolysis, but its most potent regulator. In the present review, we will summarize the work that led to its discovery and we will try to delineate its potential role in the control of metabolism in various organisms.

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Fructose 2,6-bisphosphate 2 Years After its Discovery

Fructose 2,6-bisphosphate.

Fructose 2,6-bisphosphate

Lipids are essential components of all living cells, functioning as an energy store and playing an important role in all biologic membranes. Triacylglycerols, the storage form and most abundant of the glycerolipids, represent a highly concentrated form of energy, yielding twice as many calories per gram as carbohydrate or protein. The phospholipids are amphipathic compounds which, along with cholesterol, are found in membranes where they interact to provide a polar-faced, hydrophobic continuum of critical importance for proper cell structure and function. A major function of lipogenesis is to store (as triacylglycerols) the chemical energy or foodstuffs ingested above the immediate requirements of an organism. Contrary to protein, which is not stored, and to carbohydrate, which can only be stored in limited quantities, the capacity to store triacylglycerols is almost unlimited. The ability to keep large amounts of triacylglycerols on board would not be useful, however, if it were not possible to quickly and efficiently stop diverting foodstuffs into triacylglycerol formation and to quickly and efficiently start utilizing these compounds to provide the energy necessary to synthesize ATP. For this reason, mechanisms have evolved which finely tune the synthesis and degradation of triacylglycerol to the ever changing demand for ATP. In contrast, phospholipid and cholesterol synthesis must be, at least, partially maintained (or their degradation curtailed), even in the face of limited food intake or frank starvation, to provide sufficient quantities of these lipids to fulfill their crucial role in biologic membranes. In rodents the proportion of total body fatty acids synthesized by the liver ranges from 3% (fasted animals) to 50%

Short-term Hormonal Control of Hepatic Lipogenesis

http://www.jbc.org/content/256/22/11724.full.pdf

Formation and turnover of triglyceride-rich vesicles in the chick liver cell. Effects of cAMP and carnitine on triglyceride mobilization and conversion to ketones.

M D Lane

Papers

Acute control of fatty acid synthesis by cyclic AMP in the chick liver cell: possible site of inhibition of citrate formation.