1. The activity and the kinetic properties of purified hepatic phosphorylases a and b from rabbit and rat have been investigated in the glycogenolytic direction with a radiochemical assay. 2. In contrast with the a form, phosphorylase b has an absolute requirement for both AMP and a lyotropic salt. When the latter effectors are included, the b/a-form activity ratio remains low (0.03-0.15) at the hepatic concentration of Pi, because the b form has an exceedingly low affinity for this substrate. 3. Only phosphorylase b is significantly inhibited by glucose, glucose 6-phosphate and MgATP2-. Assays in the presence of substrastes, stimulators and inhibitors in the physiological concentration range indicate that glycogenolysis in the liver depends strictly on the conversion of phosphorylase b into a. Even at 1 mM-AMP the b/a-form activity ratio does not exceed 0.01. 4. Current spectrophotometric procedures for the glycogenolytic assay of phosphorylase in crude liver preparations are highly specific for the a form; the measurement of total phosphorylase (a + b) would require impractical modifications, and is better performed in the direction of glycogen synthesis.
Skip Nav Destination
Research Article| November 15 1981
The catalytic activity of phosphorylase b in the liver. With a note on the assay in the glycogenolytic direction
Biochem J (1981) 200 (2): 327–336.
- Views Icon Views
- Share Icon Share
W Stalmans, G Gevers; The catalytic activity of phosphorylase b in the liver. With a note on the assay in the glycogenolytic direction. Biochem J 15 November 1981; 200 (2): 327–336. doi: https://doi.org/10.1042/bj2000327
Download citation file:
Don't already have an account? Register
Get Access To This Article
Buy This Article