Effect of sodium cholate on the catalytic and structural properties of phosphorylase b.
Sodium cholate at millimolar concentration is able to induce activity in rabbit muscle phosphorylase b in the absence of AMP. The maximum activation of the enzyme in presence of 7 mM sodium cholate was 24% of that achieved by 1 mM AMP. Other bile salts tested showed a negligible activating effect. The Ka for AMP was lowered fivefold by 5 mM of the steroid detergent, while the cooperative binding of the nucleotide was abolished. Phosphorylase b', a modified form of phosphorylase in which the phosphorylation site has been removed by limited tryptic attack, presented an activation profile similar to that of phosphorylase b. In contrast, phosphorylase a was inhibited by the bile salt, while the activity of liver phosphorylase b was not significantly affected. Modification of the AMP site of the enzyme with 2,3-butanedione could not inhibit sodium-cholate-induced activity. tert-Butanol, an organic solvent activator of phosphorylase b, was found to enhance the activity induced by sodium cholate. The interaction of sodium cholate and phosphorylase b was also followed by difference spectroscopy using a fluorescein isothiocyanate--phosphorylase b conjugate. Furthermore, measurements of electron spin resonance demonstrated that the mobility of a spin-label bound at buried--NH2 groups of phosphorylase b decreases cooperatively with increasing bile salt concentration.
D000249:Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D055598:Chemical Phenomena; D002621:Chemistry; D019826:Cholic Acid; D002793:Cholic Acids / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D010763:Phosphorylase b / Q000302:isolation & purification*; D006005:Phosphorylases / Q000302:isolation & purification*; D011817:Rabbits
D002793:Cholic Acids; D000249:Adenosine Monophosphate; D010763:Phosphorylase b; D006005:Phosphorylases; D019826:Cholic Acid