Caffeine inhibition of glycogen phosphorylase from Mytilus galloprovincialis mantle tissue

• Published in: The international journal of biochemistry & cell biology Vol. 27; no. 9; pp. 911 - 916
• Main Authors: Serrano, Fuencisla San Juan, López, JoséLuis Sánchez, Martín, L.Oscar Garcia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 01-09-1995
• Subjects: Adenosine Monophosphate - metabolism; Animals; Bivalvia - enzymology; Caffeine; Caffeine - pharmacology; Enzyme Inhibitors - pharmacology; Glycogen - metabolism; Inhibition; Mytilus; Phosphates - metabolism; Phosphorylase; Phosphorylase a - antagonists & inhibitors; Phosphorylase b - antagonists & inhibitors; Phosphorylases - antagonists & inhibitors; Phosphorylation; Substrate Specificity; Inhibition; Phosphorylase; Mytilus; Caffeine
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/1357-2725(95)00058-W

A different caffeine inhibition of both phosphorylated and unphosphorylated forms of glycogen phosphorylase from
Mytilus mantle has been demonstrated. Caffeine increases the allosteric constant of phosphorylase b 30-fold, acting as an allosteric inhibitor (
n
H
=2) of mixed type with respect to inorganic phosphate (Pi) and AMP, and of single competitive type with respect to glycogen. The
Mytilus phosphorylated form is also caffeine inhibited through competitive inhibition in relation to Pi and glycogen. In this case, the inhibitor does not modify the allosteric constant (near 2), neither does it display allosteric effects (
n
H
=1). The results demonstrate the notable modification of the nucleotide site promoted by the phosphorylation process and the existence of a functional inhibitory nucleoside site in
Mytilus phosphorylase.