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Modeling the biochemical differences between rabbit muscle and human liver phosphorylase
V L Rath1, C B Newgard, S R Sprang
1Department of Biochemistry and Biophysics, University of California 94143.
Proteins
|January 1, 1987
Summary
Researchers identified key amino acid changes in liver glycogen phosphorylase. These alterations explain differences in how the enzyme binds and is activated by AMP compared to the muscle isozyme.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Glycogen phosphorylases break down glycogen into glucose-1-phosphate.
- Mammalian glycogen phosphorylase exists as liver, muscle, and brain isozymes.
- Muscle isozyme binds AMP cooperatively; liver isozyme binds noncooperatively.
Purpose of the Study:
- To investigate the molecular basis for differing AMP activation between human liver and rabbit muscle glycogen phosphorylase.
- To identify specific amino acid substitutions responsible for altered AMP binding and activation.
Main Methods:
- Comparative analysis of human liver and rabbit muscle glycogen phosphorylase amino acid sequences.
- Utilized computer graphics to model structural changes.
- Interpreted biochemical differences based on structural modifications.
Main Results:
- Human liver and rabbit muscle phosphorylase share 80% sequence identity, with conserved AMP-contacting residues.
- Identified two specific amino acid substitutions in liver phosphorylase.
- These substitutions are hypothesized to alter cooperative AMP binding and activation.
Conclusions:
- Specific amino acid substitutions in liver glycogen phosphorylase explain its distinct AMP binding and activation properties.
- Understanding these differences provides insight into enzyme regulation and isozyme function.