Naturally Occurring Hexose Phosphates

A number of hexose phosphates have been isolated from natural sources. Of these oTructose 1,6-diphosphate (Harden-Young ester) (I), D-fructose 6-phosphate (Neuberg ester) (II), D-glucose 6-phosphate (Robison ester) (III), and a-D-glucose 1-phosphate (IV) are of particular biochemical importance in the processes of fermentation and glycolysis. These hexose phosphates are interconvertible in the presence of the proper enzymes and cofactors. 

The work on phosphorylated sugars was initiated by Harden and Young 

It- Robison and M. G. Macfarlane, in Methoden der Fermentforschung, (Bamann-Myrback, eds.), p. 296. Georg Thieme, Leipzig, 1941. 

The procedure consisted in allowing air- or acetone-dried yeast or yeast juice to ferment sugar in the presence of phosphate. Under these conditions phosphate becomes esterified according to the following equation  

According to the conditions, hexose monophosphate and trehalose phosphate also accumulate in varying amounts. Separation of the fructose diphosphate from the monophosphate can be effected by precipitating the diphosphate with neutral lead acetate or barium ions, followed by precipitation of the monophosphate from the supernatant liquid with basic lead acetate or barium ions in 50% or stronger ethanol (199). The separation of the different monophosphates was carried out by fractional crystallization (200). Chromatographic methods have also been used (Chapter XI). 

---

The hexose monophosphate (Helly, 1976) and pentose phosphate (Hochachka and Hayes, 1962 Yamaguchi et al., 1976 Walsh, 1985 Malinovskaya, 1988 Kudryavtseva, 1990) shunts have also been found to increase in importance. The activity of transketolase, the enzyme which inhibits the peptide-phosphate pathway, is greater in fish from cold water, e.g. trout and smelt, than in those from warm water (Kudryavtseva, 1990). In the Black Sea horse-mackerel, a sharp decline in adenine nucleotide content (AMP, ADP and ATP) in white and red muscle tissues and in liver occurs at low temperature (Trusevich, 1978). In this case, the ATP is mosdy resynthesized by glycolysis. The increase in the glucose content of the blood of fish at low ambient temperatures may be of the same nature (Prosser, 1967 ... 

---