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[Interaction of muscle glycogen phosphorylase B with flavin mononucleotide and its analogs]
Abstract:
The inhibition of rabbit skeletal muscle glycogen phosphorylase B by FMN and its analogues with substituents in the positions 6 and 8 has been studied. Inhibiting action of FMN is manifested in reducing the limiting rate of enzymic reaction and in increasing the half-saturation concentration of AMP. The inhibitor half-saturation values (in microM) increase in the following order: FMN (13,5), 6-bromo-FMN (27), 8 alpha-hydroxy-FMN (30), 8-dimethylamino(nor)-FMN (33), 6-(N-acetyl-L-cysteine-S-yl)-FMN (44), 6-amino-FMN (96), 8-hydroxy(nor)-FMN (109), 6-nitro-FMN (170), 8 alpha-(N-acetyl-L-cysteine-S-yl)-FMN (260). The existence of the glycogen phosphorylase B complexes with FMN or its analogues has been proved by spectrophotometry and sedimentation in analytical ultracentrifuge. FMN has been shown to hinder AMP-induced transition of dimeric form of the enzyme to tetrameric one. AMP at high concentrations has been found to inhibit glycogen phosphorylase B.
Insights
Flavin mononucleotide (FMN) and its analogues inhibit rabbit skeletal muscle glycogen phosphorylase B by slowing reactions and affecting enzyme structure. Modifications at positions 6 and 8 alter inhibitory potency, impacting enzyme kinetics.
Area of Science:
- Biochemistry
- Enzymology
Context:
- Rabbit skeletal muscle glycogen phosphorylase B is a key enzyme in glycogen metabolism.
- Flavin mononucleotide (FMN) and its analogues are investigated as potential modulators of enzyme activity.
Purpose:
- To study the inhibitory effects of FMN and its analogues on rabbit skeletal muscle glycogen phosphorylase B.
- To elucidate the structure-activity relationships of FMN analogues substituted at positions 6 and 8.
Summary:
- FMN and its analogues inhibit glycogen phosphorylase B by reducing the reaction rate and increasing the AMP half-saturation concentration.
- Inhibitor potency varies with substituents, with 6-bromo-FMN and 8-alpha-hydroxy-FMN showing significant inhibition.
- Complex formation between the enzyme and FMN analogues was confirmed via spectrophotometry and ultracentrifugation, demonstrating FMN's role in hindering AMP-induced conformational changes.
Impact:
- Provides insights into the allosteric regulation of glycogen phosphorylase B.
- Identifies specific FMN analogues with potential for modulating glycogenolysis.
- Contributes to understanding enzyme inhibition mechanisms and drug design for metabolic disorders.