Journal of Biochemistry Advance Access originally published online on June 23, 2006
Journal of Biochemistry 2006 140(1):135-140; doi:10.1093/jb/mvj129
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© 2006 The Japanese Biochemical Society.
Regular Paper |
Activation of 4-
-Glucanotransferase Activity of Porcine Liver Glycogen Debranching Enzyme with Cyclodextrins
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, 2-1 Daisen-cho, Sakai, Osaka 590-0035
* To whom correspondence should be addressed. Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 590-0035. Tel: +81-72-222-4811, Fax: +81-72-222-4791, E-mail: komichi{at}center.osaka-wu.ac.jp
Glycogen debranching enzyme (GDE) is a single polypeptide chain containing distinct active sites for 4-
-glucanotransferase and amylo--1,6-glucosidase activities. Debranching of phosphorylase limit dextrin from glycogen is carried out by cooperation of the two activities. We examined the effects of cyclodextrins (CDs) on debranching activity of porcine liver GDE using a fluorogenic branched dextrin, Glc1-4Glc1-4Glc1-4(Glc1-4Glc1-4Glc1-4Glc1-6)Glc1-4Glc1-4Glc1-4Glc1-4GlcPA (B5/84), as a substrate. B5/84 was hydrolyzed by the hydrolytic action of 4--glucanotransferase to B5/81 and maltotriose. The fluorogenic product was further hydrolyzed by the amylo--1,6-glucosidase activity to the debranched product, Glc1-4Glc1-4Glc1-4Glc1-4Glc1-4Glc1-4Glc1-4GlcPA (G8PA), and glucose. -, ß- and 
-CDs accelerated the liberation of B5/81 from B5/84, indicating that the 4--glucanotransferase activity was activated by CDs to remove the maltotriosyl residue from the maltotetraosyl branch. This led to acceleration of B5/84 debranching. The extent of 4--glucanotransferase activation increased with CD concentration before reaching a constant value. This suggests that there is an activator binding site and that the binding of CDs stimulates 4--glucanotransferase activity. In the porcine liver, glycogen degradation may be partially stimulated by the binding of a glycogen branch to this activator binding site.
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