Glycogen metabolism: the integrated cellular response to a bi-directional metabolic stimulus.

The control exerted by phosphorylase a over the I-conversion of glycogen synthase (1) does not apply to glycogen synthesis, as judged from experiments with intact human leucocytes. 1. In incubated leucocytes conversion of glycogen synthase (GS) (E.C.2.4.1.11) to GS-I is preceeded by inactivation of glycogen phosphorylase a (GPh-a). 2. By the addition of latex particles a flash-activation of GPh-a can be elicited within 10–30 sec. in the intact cells. 3. GPh is inactivated when a glucose load is given. 4. When, in glycogen depleted cells, glucose is given immediately after latex the I-conversion of GS is completely abolished, and GS-I remains low for 20 min although GPh is rapidly inactivated after the glucose is given. 5. However, glycogen synthesis as compared with a control in which only glucose is given, and in which a large I-conversion occurs, is not the least depressed. 6. This apparent contradiction is completely resolved taking into account a newly discovered, intermediate form of GS (2) (GS-R). 7. An important physiological role can be proposed for GS-R.