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Maize Root Phytase (Purification, Characterization, and Localization of Enzyme Activity and Its Putative Substrate)
1Universitat Bayreuth, Botanisches Institut, Universitatsstrasse 30, 95440 Bayreuth, Germany.
Plant Physiology
|December 1, 1996
Summary
Researchers purified three phytase isoforms from maize roots, revealing their molecular properties and substrate specificity. Phytase activity was localized in the endodermis, with phytate identified as the native substrate.
Area of Science:
- Biochemistry
- Plant Science
- Enzymology
Background:
- Phytases (EC 3.1.3.26) are crucial enzymes involved in phosphorus metabolism.
- Understanding phytase isoforms in crops like maize (Zea mays L.) is important for agricultural applications.
- Maize roots contain phytase activity, but its specific isoforms and localization require detailed characterization.
Purpose of the Study:
- To isolate and purify phytase isoforms from maize seedlings.
- To characterize the biochemical properties, including molecular mass, isoelectric points, and kinetic parameters, of these isoforms.
- To determine the substrate specificity and localization of phytase activity within maize roots.
Main Methods:
- Purification of phytase isoforms from 8-day-old maize (Zea mays L. var Consul) seedlings.
- Determination of molecular mass, isoelectric points, and subunit composition.
- Enzyme kinetics analysis using sodium inositol hexakisphosphate (phytate) and 4-nitrophenyl phosphate as substrates.
- Identification of hydrolysis intermediates and localization studies using root slices.
Main Results:
- Three phytase isoforms were purified with native molecular mass of 71 kD and subunit mass of 38 kD.
- Isoelectric points ranged from pH 4.8 to 5.0, with optimal activity at 40°C and pH 5.0.
- Apparent Michaelis constants for phytate were low (24–43 μM), with higher values for 4-nitrophenyl phosphate (137–157 μM).
- Phytate hydrolysis followed a nonrandom pathway, yielding specific intermediates.
- Phytase activity was localized to the endodermis of maize roots, distinct from general phosphatase activity.
Conclusions:
- Maize roots possess distinct phytase isoforms with specific biochemical characteristics.
- Phytate is confirmed as the likely native substrate for these maize root phytases.
- The endodermal localization suggests a specific role for phytase in maize root physiology and phosphorus uptake.