Final answer:
Phosphorylase b is more active than phosphorylase a when there is a demand for energy in a cell, as signaled by hormones, resulting in a phosphorylation cascade that activates phosphorylase b. However, when there is adequate energy available, as indicated by high ATP levels, phosphorylase b remains inactive.
Step-by-step explanation:
The conditions when phosphorylase b is more active than phosphorylase a relate to the metabolic state of the cell pertaining to energy requirements and hormonal signals. Phosphorylase b, the inactive form of glycogen phosphorylase, is converted into the active form, phosphorylase a, in response to hormones like epinephrine and glucagon, which signal a requirement for energy. The conversion involves the activation of a cascade that includes the enzyme adenyl cyclase, the production of cyclic AMP (cAMP), and the subsequent activation of protein kinase A (PKA). PKA activates phosphorylase kinase, which in turn phosphorylates phosphorylase b, converting it to phosphorylase a. Phosphorylase a then catalyzes the breakdown of glycogen to glucose-1-phosphate, providing energy. In contrast, when there is adequate energy in the cell, indicated by high levels of ATP, the conversion to glucose is not necessary, and phosphorylase b remains inactive.