To examine the accessibility of the enzyme cellodextrin phosphorylase (CDP) towards multivalent cluster carbohydrates, the cellobiosylated dimer 10 and trimer 12, as well as the cellobiose-coated PAMAM dendrimers 14, 16, 18, 20 and 22, with four, eight, sixteen, thirty-two and sixty-four cellobiose units at the outer surface of PAMAM dendrimers, respectively, have been synthesized for the first time and used as acceptor substrates for the enzyme CDP. It was found that CDP was able to transfer a glucosyl moiety from glucose-1-phosphate (Glc-1-P) into these synthesized cluster cellobiosylated glycoconjugates and cellobiose-coated PAMAM dendrimers, which were thus acceptor substrates for CDP. It was found that the ability of CDP to interact with smaller cellobiosylated glyconjugates and with PAMAM dendrimers containing up to eight cellobiose units was similar to that seen with cellobiose. However, this capability of CDP was somewhat lessened with the PAMAM dendrimer containing sixteen cellobiose moieties and dramatically decreased towards PAMAM dendrimers with thirty-two and sixty-four cellobiose units. This might be due to their steric bulk, CDP enzyme no longer being able to hold them properly on its active site. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).