Studies on Starch Phosphate Part 1. Estimation of glucose‐6‐phosphate residues in starch and the presence of other bound phosphate(s)

Abstract The phosphorus of glucose‐6‐phosphate residue in starch (P(G6P)) was estimated specifically by means of glucose‐6‐phosphate dehydrogenase (E.C.1.1.1.49) after acid hydrolysis. Sixty to 70 % of total phosphorus in potato starch was found to be P(G6P)). It was shown that the rest of phosphorus (Px) was incorporated as glucose‐2‐phosphate and/or glucose‐3‐phosphate, since it was determined as glucose by periodate oxidation, borohydride reduction, acid hydrolysis and treatment with alkaline phosphatase. The Px was more labile to acid and heat than P(G6P) and decomposed yielding inorganic phosphate. The phospholigosacharide ( D. P. 3.6), which was prepared by the limit hydrolysis of potato starch with glucoamylase of Rh. delemar (α‐1,4‐Glucan glucohydrolase E.C.3.2.1.3) was fractionated by gel‐filtration through Sephadex G‐25 into fractions with D.P. 2 to 7. Each fraction contained a mole of phosphorus per mole of the saccharide. The P(G6P) and the Px were enriched in the low and the high D.P. fractions, respectively.