[Allosteric properties of phosphorylase b].

Area of Science:

• Biochemistry
• Enzymology
• Protein Conformation

Background:

• Skeletal muscle phosphorylase b is a key enzyme in glycogen metabolism.
• This enzyme exists in different conformational states, influencing its activity.
• Understanding these states is crucial for comprehending metabolic regulation.

Purpose of the Study:

• To investigate the existence of distinct forms of phosphorylase b in different mammalian skeletal muscles.
• To characterize the kinetic and physico-chemical properties of these forms.
• To explore the relationship between enzyme conformation and tissue-specific metabolic characteristics.

Main Methods:

• Affinity chromatography using AMP-Sepharose.
• Elution with glucose-6-phosphate and adenosine monophosphate (AMP).
• Kinetic assays and analysis of SH-group reactivity.

Main Results:

• Rabbit and bovine muscle phosphorylase b separated into two distinct fractions based on elution profiles.
• Fractions eluted by glucose-6-phosphate and AMP exhibited different kinetic properties and SH-group reactivity.
• AMP-eluted forms showed resistance to glucose-6-phosphate inhibition.

Conclusions:

• Phosphorylase b exists in at least two distinct forms in skeletal muscle.
• These forms likely represent different conformational states (R and T states).
• The equilibrium between these conformations is influenced by the metabolic context of the tissue.