Open AccessEvidence for Precursor Forms of the Low Isoelectric Point α-Amylase Isozymes Secreted by Barley Aleurone Cells
Author(s) -
John V. Jacobsen,
Douglas Bush,
Lilianne Sticher,
Russell L. Jones
Publication year - 1988
Publication title -
plant physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.554
H-Index - 312
eISSN - 1532-2548
pISSN - 0032-0889
DOI - 10.1104/pp.88.4.1168
Subject(s) - isozyme , isoelectric point , aleurone , hordeum vulgare , biochemistry , isoelectric focusing , extracellular , biology , glycosylation , intracellular , amylase , enzyme , microbiology and biotechnology , botany , poaceae
Gibberellin-treated barley (Hordeum vulgare L.) aleurone cell protoplasts have been shown previously to contain two alpha-amylase isozymes which are not secreted (JV Jacobsen, JA Zwar, PM Chandler 1985 Planta 13: 430-438). This report shows that these intracellular forms are immunochemically related to the low isoelectric point but not the high isoelectric point group of alpha-amylase isozymes and that they arise by new synthesis like the secreted forms. Pulse-chase studies show that the intracellular isozymes are precursors to the secreted isozymes. Conversion of the intra- to the extracellular forms involves decreases in isoelectric points with no change in size detectable by SDS-PAGE. The precursor isozymes were also detected in aleurone layer homogenates but they were unstable. They could be stabilized by various treatments including heating the homogenate to 70 degrees C for 10 minutes indicating that the instability was enzymically mediated. Using purified radioactive precursor isozymes, it was shown that instability did not involve inactivation but the conversion to secreted forms. The nature of the covalent modification associated with conversion was not determined but available data indicate that it does not involve glycosylation.