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Kinetic studies on muscle glycogen synthase
The Journal of Biological Chemistry
|May 10, 1975
Summary
Rabbit muscle glycogen synthase follows a sequential mechanism, with UDP-glucose and glycogen/maltose kinetics revealing distinct substrate affinities. This clarifies the enzyme's action in glycogen synthesis.
Area of Science:
- Biochemistry
- Enzymology
- Metabolic pathways
Background:
- Glycogen synthase is a key enzyme in glycogen synthesis.
- Understanding its kinetic mechanism is crucial for metabolic research.
Purpose of the Study:
- To investigate the kinetics and mechanism of rabbit muscle glycogen synthase.
- To determine the enzyme's substrate interactions with UDP-glucose and acceptors like glycogen and maltose.
Main Methods:
- Enzyme kinetics assays using the I form of glycogen synthase.
- Bisubstrate kinetic analysis with UDP-glucose and varying acceptors (glycogen, maltose).
- Double reciprocal plot analysis to determine reaction mechanisms.
Main Results:
- No evidence of UDP-glucose exchange with [14C]UDP was observed.
- Bisubstrate kinetics indicated a sequential reaction mechanism (ordered or random).
- The Michaelis constant (K-m) for UDP-glucose was consistent (45-48 mM) with both maltose and glycogen.
- Distinct K-m values were found for maltose (230 mM) and glycogen (1.5 µg/ml).
Conclusions:
- Rabbit muscle glycogen synthase operates via a sequential mechanism.
- The enzyme exhibits different affinities for maltose and glycogen as substrates.