Specific maltose labeling in the reducing glucose moiety.

Radioactive maltose with label in the reducing glucose moiety was prepared using a glucosyltransferase enzyme to catalyze exchange of 6-³H]glucose into unlabeled maltose. The enzyme was isolated from spinach by ammonium sulfate precipitation followed by DEAE column chromatography. A 77% yield of 6-³H]maltose was obtained after a reaction of 100 nmol of maltose with 0.0147 nmol of 6-³H]glucose was catalyzed by the most active column peak. The product was exclusively labeled in the reducing glucose moiety as indicated by the label occurring only in sorbitol following sodium borohydride reduction and sulfuric acid hydrolysis. Between 88.3 and 96.0% of the tritium in the synthesized preparation was present as 6-³H]maltose by Dowex 1-X4 chromatography. This column separates 6-³H]maltose-U-¹⁴C]maltose mixtures and 6-³H]glucose-U-¹⁴C]glucose mixtures apparently as a result of an isotope effect.