Hormonal effects on the phosphorylation of glycogen synthase in rat hepatocytes

The effects of epinephrine and vasopressin on the phosphorylation state of glycogen synthase were studied using rat hepatocytes incubated with 32P. After the incubation with hormones, 32P-labeled glycogen synthase was isolated using antibodies against rat liver enzyme. The immunoprecipitate showed a single radioactive band ( Mapp 88 kDa) when subjected to SDS-gel electrophoresis. Both epinephrine and vasopressin inactivated the enzyme and increased the 32P content of glycogen synthase. Cleavage of the immunoprecipitate with CNBr yielded two major 32P-labeled fragments of Mapp approximately 27 and 12 kDa. Both hormones increased the 32P content of both fragments. These results prove that epinephrine and vasopressin increase the phosphate content of the enzyme promoting its phosphorylation at multiple sites.

Different effects of glucagon and epinephrine on the kinetic properties of liver glycogen synthase

Kinetic constants of glycogen synthase (M0.5 for glucose-6-P and S0.5 for UDP-glucose) were determined after hepatocytes isolated from starved rats were incubated with either glucagon or epinephrine. Incubation with these hormones resulted in an increase in both S0.5 and M0.5. However, the action of glucagon resulted in great modifications on S0.5 whereas epinephrine affected mainly M0.5. Therefore, glucagon and epinephrine alter the kinetic properties of glycogen synthase provoke the phosphorylation of glycogen synthase at different site(s) acting through different mechanisms.

The Proton Microprobe: A Powerful Tool for Nondestructive Trace Element Analysis

A proton microprobe capable of focusing proton beams with energies up to 6 million electron volts to a spot size of 2 x 2 square micrometers has been used for chemical analysis of small grains of minerals in lunar samples by proton-induced x-ray emission. The proton microprobe is preferable to the electron microprobe for analyzing trace elements whose concentrations are below the detection limit of the latter and for analyzing objects with numerous major and trace elements with a wide range of atomic numbers. Application of the proton microprobe to biological samples is feasible.