Phosphorylase action

Unbranched (aI—>4) polymer substrate for further phosphorylase action... 

Hydrogen-ion concentration effect on enzyme kinetics, 292, 327 on phosphorylase action, 355 mutarotation measurement by, 52... 

It was not until tlie 1960s that it became quite clear that, in the living cell, glycogen synthesis followed quite another and more complicated route than the reversal of phosphorylase action, and that in this new pathway the equilibrium of the reaction was shifted decisively away from the sugar phosphate and towards the polymer chain formation. This breakthrough followed the discovery by Luis Leloir in Argentina of a new coenzyme derived from the pyrimidine, uracil. 

Despite continued and intensive research, the mechanism of phosphorylase action is not known, although the formation of an intermediary n-glucosyl-enzyme complex is now considered to be imlikely the role of pyridoxal 5-phosphate and the mode of activation by adenosine 5-phosphate are also unknown. The fact that adenosine 5-phosphate lowers the energy of activation of phosphorylase a suggests that it may be situated near to the active center, and further, that each molecule of phosphorylase a may contain four active centers. ... 

The phosphorolytic enzymes at present are usually classed together. As noted above, these do not insert the elements of water but phosphoric acid instead. So far, no phosphates other than sugar phosphates have been the products of phosphorylase action which may be formulated by analogy with the carbohydrates ... 

Muscle also contains an amylo-1,6-glucosidase which hydrolyzes the l,6 -a-glucoside links of the limit dextrin obtained from phosphorylase action on glycogen or amylopectin. The products of the reaction are glucose and a dextrin which can further be partially phosphorolyzed by the phosphorylase. 

In non-lethal experimented CO poisoning there is marked decrease of glycogen with concommitant increase of lactate, indicating accelerated carbohydrate catabolism [44]. Glycogen phosphorylase which catabolizes the transformation into glucose-1-phosphate does, however, not show any increased activity. AMP which activates phosphorylase B (dephosphory-lase) is increased by 50%. Cyclic AMP, which stimulates the conversion of phosphorylase B to A in liver preparations [45] and is one of the controlling factors in phosphorylase activation in liver and skeletal muscle, has not been investigated as to its involvement in the control of brain phosphorylase action [46]. 

---