Of the four chloroplast β-amylase (BAM) proteins identified in Arabidopsis, BAM3 and BAM4 were previously shown to play the major roles in leaf starch breakdown, although BAM4 apparently lacks key active site residues and β-amylase activity. Here we tested multiple BAM4 proteins with different N-terminal sequences with a range of glucan substrates and assay methods, but detected no α-1,4-glucan hydrolase activity. BAM4 did not affect BAM1, BAM2 or BAM3 activity even when added in 10-fold excess, nor the BAM3-catalysed release of maltose from isolated starch granules in the presence of glucan water dikinase. However, BAM4 binds to amylopectin and to amylose–Sepharose whereas BAM2 has very low β-amylase activity and poor glucan binding. The low activity of BAM2 may be explained by poor glucan binding but absence of BAM4 activity is not. These results suggest that BAM4 facilitates starch breakdown by a mechanism involving direct interaction with starch or other α-1,4-glucan.

Item Type:	Refereed Article
Keywords:	catalyst, starch, arabidopsis thaliana
Research Division:	Biological Sciences
Research Group:	Plant Biology
Research Field:	Plant Physiology
Objective Division:	Expanding Knowledge
Objective Group:	Expanding Knowledge
Objective Field:	Expanding Knowledge in the Biological Sciences
UTAS Author:	Smith, SM (Professor Steven Smith)
ID Code:	101476
Year Published:	2009
Web of Science® Times Cited:	17
Deposited By:	Plant Science
Deposited On:	2015-06-24
Last Modified:	2015-09-22
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