Running head: Phosphorylation of A- and B-type crystallized maltodextrins

138 In this study, two crystallized maltodextrins were generated that consist of the same 139 oligoglucan pattern but differ strikingly in the physical order of double helices. As revealed 140 by X-ray diffraction, they represent the highly ordered Aor B-type allomorph. Both 141 crystallized maltodextrins were similar in size distribution and birefringence. They were used 142 as model substrates to study the consecutive action of the two starch-related dikinases, the 143 glucan, water dikinase and the phosphoglucan, water dikinase. The glucan, water dikinase 144 and the phosphoglucan, water dikinase selectively esterify glucosyl residues in the C6 and C3 145 position, respectively. Recombinant glucan, water dikinase phosphorylated both allomorphs 146 with similar rates and caused complete glucan solubilization. Soluble neutral maltodextrins 147 inhibited the glucan, water dikinase-mediated phosphorylation of crystalline particles. 148 Recombinant phosphoglucan, water dikinase phosphorylated both the Aand the B-type 149 allomorph only following a prephosphorylation by the glucan, water dikinase and the activity 150 increased with the extent of prephosphorylation. The action of the phosphoglucan, water 151 dikinase on the prephosphorylated Aand B-type allomorphs differed. When acting on the B152 type allomorph, by far more phosphoglucans were solubilized as compared to the A-type. 153 However, with both allomorphs the phosphoglucan, water dikinase formed significant 154 amounts of monophosphorylated phosphoglucans. Thus, the enzyme is capable of acting on 155 neutral maltodextrins. It is concluded that the actual carbohydrate substrate of the 156 phosphoglucan, water dikinase is defined by physical rather than by chemical parameters. A 157 model is proposed that explains, at a molecular level, the consecutive action of the two starch158 related dikinases. 159 160 16