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Two types of phosphorylase from etiolated soybean cotyledons
M Suda1, T Watanabe, M Kobayashi
1Department of Agricultural Chemistry, Faculty of Agriculture, Tohoku University, Miyagi.
Journal of Biochemistry
|September 1, 1987
Summary
Soybean cotyledons contain two distinct phosphorylase enzymes (I and II) with different molecular weights and substrate specificities. These enzymes exhibit properties similar to cytoplasmic and chloroplastic plant leaf phosphorylases, respectively.
Area of Science:
- Biochemistry
- Plant Physiology
- Enzymology
Background:
- Phosphorylases are key enzymes in carbohydrate metabolism, involved in glycogen and starch breakdown.
- Plant tissues contain multiple phosphorylase isoforms with potentially distinct roles and localization.
Purpose of the Study:
- To isolate and characterize two distinct phosphorylase isozymes from etiolated soybean cotyledons.
- To compare their biochemical properties, including molecular weight, substrate specificity, and kinetic parameters.
- To determine their potential relationship to known plant phosphorylase types.
Main Methods:
- Column chromatography on DEAE-Sephacel for enzyme separation and purification.
- Electrophoretic analysis (Hedrick and Smith method) to assess protein distinctness.
- Determination of kinetic parameters (Km values) using various substrates like glucose 1-phosphate, glycogen, and maltoheptaose.
Main Results:
- Two phosphorylases (I and II) were purified, with subunit molecular weights of 100,000 and 113,000, respectively.
- Enzyme I (dimer) showed higher activity with longer glucan chains, while Enzyme II (tetramer) preferred shorter maltooligosaccharides.
- Kinetic parameters (Km) differed significantly between the two enzymes for the tested substrates.
- Electrophoresis confirmed that phosphorylases I and II are distinct proteins.
Conclusions:
- Soybean phosphorylases I and II are distinct isozymes with differential substrate preferences.
- Phosphorylase I exhibits characteristics similar to a cytoplasmic plant phosphorylase.
- Phosphorylase II shows properties analogous to a chloroplastic plant phosphorylase, suggesting specialized roles in carbohydrate metabolism.