Abstract
The protein fraction extracted with a high ionic strength buffer from the cell wall preparation of oat (Avena sativa L.) coleoptiles and first leaves contained starch-degrading (amylase) activity. The activity of apoplastic amylase in the coleoptiles and first leaves continued to increase in parallel with organ growth. One of the apoplastic amylases recovered from shoot cell wall preparations was purified by sequential ion exchange and gel filtration chromatography, and the catalytic properties of the enzyme were analysed. The purified enzyme gave a single 25 kDa protein band on SDS-PAGE. The enzyme exhibited maximum activity at pH 5.0 against maltooligosaccharides. The purified enzyme hydrolysed soluble starch and maltooligosaccharides larger than tetraose at maltose unit, but did not hydrolyse beta-limit dextrin or p-nitrophenyl-alpha-d-glucopyranoside. These results as well as the findings that the molecular size and the catalytic properties of the purified enzyme are different from those of known amylases obtained from Gramineae caryopses suggest that this enzyme is a novel type of beta-amylase present in cell walls of vigorously elongating Gramineae shoot organs.
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