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Metabolism and Enzymology

Characterization of D-Enzyme (4--Glucanotransferase) in Arabidopsis Leaf ¹

Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824

Two major forms of D-enzyme (4--glucanotransferase, EC 2.4.1.25) were successfully separated from most of the amylase activity using FPLC-Mono Q column chromatography. Transfer of a maltosyl group was observed upon the incubation of D-enzyme with maltotriose and D-[U-¹⁴ C]glucose. About 4.5% of the radioactivity was transferred to maltotriose in 2 hours. End product analysis showed the accumulation of glucose and maltopentaose from maltotriose within the first 10 minutes of the reaction. Several other maltodextrins were also observed with longer incubation times, although maltose was never produced. A quantitative measurement of maltodextrin production from the reaction of [¹⁴ C]maltotriose with D-enzyme showed that the quantity of maltotriose decreased from 100% to 31% after 3 hours incubation, while glucose, maltotetraose, maltopentaose, maltohexaose, maltoheptaose, maltooctaose, and higher maltodextrins increased in amount. Glucose is the major product throughout the course of the reaction of D-enzyme with maltotriose. Maltotriose, in addition to glucose, are the major products in the reaction of D-enzyme with maltodextrins with a chain length greater than maltotriose. This study confirms the existence of a transglycosylase that disproportionates maltotriose and higher maltodextrins by transferring maltosyl or maltodextrinyl groups between maltodextrins resulting in the production of glucose and different maltodextrins, but not maltose, in leaf tissue with enzymic properties very similar to the previously reported D-enzyme in potato.

¹ Supported in part by National Science Foundation Grants DMB 85-10088 and 86-10319.

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