Amylopectin phosphoric acid

The phosphoric acid is not evenly distributed over the whole starch substance amylose is free or almost free from phosphorus.It may be mentioned that amylose prepared according to Ling is reported to have a very low phosphorus content. The author has obtained such preparations in some cases, but for the most part preparations were obtained which had the same or a higher phosphorus content than the starch. These preparations were not completely saccharified by /3-amylase and obviously contained amylopectin even if the solutions had a low viscosity. 

SolubUity differences of the triacetates of the purified starch fractions have not yet been investigated in detail. It might be expected, however, that amylose triacetates, which are composed of linear molecules capable of close packing, would be more insoluble than the somewhat loosely packed molecules of amylopectin triacetate. Furthermore, various amylose triacetates, because of their uniform composition, might be expected to show similar solubilities, whereas different amylopectin triacetates, due to the variation of their phosphoric acid contents, might show dissimilar solubilities. 

Amylopectin of potato starch and probably amylopectin of other tuber starches occurs as a natural ester of phosphoric acid. Potato amylopectin" contains approximately 0.07-0.09% phosphorus, " or one phosphate group for every 212 to 273 anhydroglucose units. The phosphate appears to be attached mainly to the primary alcohol group since, on hydrolysis, potato amylopectin (separated by electrodialysis)... 

The degree of polymerization of amylopectin (wheat) lies in the range of 3 x 10 -3 x 10 glucose units, which corresponds to a molecular mass of 5 X 10 -5 X 10. One phosphoric acid residue is found for an average of 400 glucose residues. 

An amylopectin molecule (4-138) consists of chains of D-glucose units linked by a-(1 4) linkages (maltose polymer), which is branched after 10 to 100 (average of 25) units by non-random a-(1 6) side chains (building unit is isomaltose). Occasionally there may also be an a-(1 3) bond (building unit of this biose is laminaribiose). One of about 400 glucose residues is esterified with phosphoric acid. 

Glycogen is an a-glucan that contains more than 10 D-glucose residues linked by a-(1 4) bonds. In every 8-12 glucose residues, side chains of other a-(1 4) glucans are bound, attached by a-(1 6) bonds, similar to as in amylopectin, but the glycogen molecule is more branched and structurally more compact. Glycogen contains also phosphoric acid in small amounts. 

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