Details

Autor(en) / Beteiligte

• Sun, Z. (Schreier Malting Co., Sheboygan, WI.)
• Duke, S.H
• Henson, C.A

Titel

The role of pea chloroplast alpha-glucosidase in transitory starch degradation

Ist Teil von

• Plant physiology (Bethesda), 1995-05, Vol.108 (1), p.211-217

Ort / Verlag

Rockville, MD: American Society of Plant Physiologists

Erscheinungsjahr

1995

Link zum Volltext

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Pea chloroplastic alpha-glucosidase (EC 3.2.1.20) involved in transitory starch degradation was purified to apparent homogeneity by ion exchange, reactive dye, hydroxylapatite, hydrophobic interaction, and gel filtration column chromatography. The native molecular mass and the subunit molecular mass were about 49.1 and 24.4 kD, respectively, suggesting that the enzyme is a homodimer. The enzyme had a Km of 7.18 mM for maltose. The enzyme's maximal activity at pH 7.0 and stability at pH 6.5 are compatible with the diurnal oscillations of the chloroplastic stromal pH and transitory starch accumulation. This pH modulation of the alpha-glucosidase's activity and stability is the only mechanism known to regulate starch degradative enzymes in leaves. Although the enzyme was specific for the alpha-D-glucose in the nonreducing end as the glycon, the aglycon moieties could be composed of a variety of groups. However, the hydrolysis rate was greatly influenced by the aglycon residues. Also, the enzyme could hydrolyze glucans in which carbon 1 of the glycon was linked to different carbon positions of the penultimate glucose residue. The ability of the alpha-glucosidase to hydrolyze alpha-1,2- and alpha-1,3-glucosidic bonds may be vital if these bonds exist in starch granules because they would be barriers to other starch degradative enzymes. This purified pea chloroplastic alpha-glucosidase was demonstrated to initiate attacks on native transitory chloroplastic starch granules