Abstract
alpha-Amylases (EC 3.2.1.1) secreted by the aleurone layer of barley grains are Ca2+-containing metalloenzymes. We studied the effect of Ca2+ on the activity and structure of the two major groups of aleurone alpha-amylase by incubating affinity purified enzyme in solutions containing Ca2+ from pCa 4 to 7. Both groups of isoforms required one atom of Ca2+/molecule of enzyme as determined by isotope exchange, but the two groups differed by more than 10-fold in their affinity for Ca2+. Both groups of alpha-amylase were irreversibly inactivated by incubation in low Ca2+ (pCa 7). This inactivation was not due to changes in primary structure, as measured by molecular weight, but appeared to be the result of changes in secondary and tertiary structure as indicated by circular dichroism spectra, serology, lability in the presence of protease, and fluorescence spectra. Analysis of the predicted secondary structure of barley aleurone alpha-amylase indicates that the Ca2+-binding region of barley amylases is structurally similar to that of mammalian alpha-amylases. Our data indicate that micromolar levels of Ca2+ are required to stabilize the structure of barley alpha-amylases in the endoplasmic reticulum of the aleurone layer where these enzymes are synthesized.
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Claims 6
Claim · model-written summary
Both barley amylase isoform groups required one calcium atom per enzyme molecule.
- Taxon
- barley
.jpg?width=60)
Hordeum vulgaret0 - Gene
- α-amylaset0
- Outcome
- required one atom of Ca2+/molecule of enzymee0
- Value
- one atom of Ca2+/molecule of enzymee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
.jpg?width=500)
Verbatim
e0“Both groups of isoforms required one atom of Ca2+/molecule of enzyme”
t0“barley aleurone α-amylase”
Claim · model-written summary
The two barley amylase groups differed in calcium affinity by more than tenfold.
- Taxon
- barleyHordeum vulgaret0
- Outcome
- affinity for Ca2+e0
- Direction
- differede0
- Value
- more than 10-folde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the two groups differed by more than 10-fold in their affinity for Ca2+”
t0“barley aleurone α-amylase”
Claim · model-written summary
Low calcium irreversibly inactivated both barley amylase groups.
- Taxon
- barleyHordeum vulgaret0
- Treatment
- incubation in low Ca2+ (pCa 7)e0
- Outcome
- alpha-amylasee0
- Direction
- irreversibly inactivatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Both groups of alpha-amylase were irreversibly inactivated by incubation in low Ca2+ (pCa 7)”
t0“barley aleurone α-amylase”
Claim · model-written summary
Inactivation appeared linked to changes in secondary and tertiary structure, not primary structure.
- Taxon
- barleyHordeum vulgaret0
- Outcome
- inactivatione0
- Qualifier
- changes in secondary and tertiary structuree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This inactivation was not due to changes in primary structure, as measured by molecular weight, but appeared to be the result of changes in secondary and tertiary structure”
t0“barley aleurone α-amylase”
Claim · model-written summary
The predicted calcium binding region of barley amylase resembles that of mammalian amylase.
- Taxon
- barleyHordeum vulgaree0
- Outcome
- Ca2+-binding regione0
- Comparator
- mammalian alpha-amylasese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the Ca2+-binding region of barley amylases is structurally similar to that of mammalian alpha-amylases”
Claim · model-written summary
Micromolar calcium is required to stabilize barley amylases in the aleurone endoplasmic reticulum.
- Taxon
- barleyHordeum vulgaree0
- Organ / stage
- aleurone layere0
- Outcome
- stabilize the structure of barley alpha-amylasese0
- Qualifier
- micromolar levels of Ca2+e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“micromolar levels of Ca2+ are required to stabilize the structure of barley alpha-amylases in the endoplasmic reticulum of the aleurone layer”