STARCH BOUND PHOSPHATE IN POTATO AS STUDIED BY A SIMPLE METHOD FOR DETERMINATION OF ORGANIC PHOSPHATE AND P-31-NMR

A simple, high capacity procedure has been developed for determination of phosphate bound to carbon atom 6 of the glucose residues (C-6 bound P) in potato starch. The procedure is based on enzymatic analysis and the use of a microplate reader. Analysis of 26 different potato cultivars shows that the total amount of bound phosphate can be deduced from the measured content of C-6 bound P. Using the simplified procedure to assay for C-6 bound P the degree of phosphorylation is shown to increase approximately 50% from the cortex to the pith of the potato tuber. Analysis of individual tubers from several plants shows that plant to plant variation with respect to the degree of phosphorylation was small and reflected tuber to tuber variation within single plants. Starch bound phosphate was also analysed by P-31-NMR. By omitting H-1-decoupling the major signal observed in spectra of gelatinized, amylase treated, and acid hydrolysed samples is unambiguously shown to represent C-6 bound phosphate.