joyb

How to Teach Quantum Physics to Your Dog, Chad Orzel

I realise that liver glycogen phosphorylase is allosterically regulated by glucose, and is generally in the phosphorylated active form when glucose levels are low, but the textbooks (both Stryer and Voet and Voet) are ambiguous at to whether the liver isozyme is covalently modified by the signalling cascade triggerred by glucagon, or whether this only applies to the muscle isozyme. It is implied that the phosphorylated 'a' form is the "default" state of the enzyme, which will break down glycogen unless signalled otherwise; is this telling me that the enzyme will be active regardless of whether glucagon is present, or will some glucagon be necessary to maintain the enzyme in its phosphorylated state?