The hepatic glycogenolysis induced by reversible ischaemia or KCN is exclusively catalysed by phosphorylase a

Abstract

1. Ischaemia was applied for 30 min to the liver of Wistar rats and of gsd/gsd rats, which have a genetic deficiency of phosphorylase kinase. The rate of glycogenolysis corresponded closely to the concentration of phosphorylase a. The loss of glycogen from Wistar livers was accounted for by the intrahepatic increase in glucose plus lactate. Further, the accumulation of oligosaccharides was negligible in the gsd/gsd liver. 2. Isolated hepatocytes from Wistar and gsd/gsd rats were incubated for 40 min in the presence of either KCN or glucagon. Again, the production of glucose plus lactate was strictly dependent on the presence of phosphorylase a. However, the catalytic efficiency of phosphorylase a was about 2-fold higher in the presence of KCN. 3. We conclude that the hepatic glycogenolysis induced by anoxia and by KCN is solely mediated by phosphorylase a. The higher catalytic activity of phosphorylase a under these circumstances could be due to an increased concentration of the substrate Pi.

Protein kinase Cϵ interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

“…138 h) [61], which brings into question how irreversible inhibition of CO could be protective in the long term, as subsequent aerobic respiration would then be inhibited. In addition, 120 µM blood levels of cyanide are fatal in man [62], and KCN potently inhibits other enzymes, including carbonic anhydrase [63], superoxide dismutase [64], phosphorylase [65] and several gluco-and galacto-sidases [66]. There has also been a report suggesting that KCN inhibits stimulusinduced mobility shifts (suggestive of autophosphorylation) of the PKCα, PKCβ 2 and PKCε isoenzymes in smooth muscle cells [67].…”

Molecular mode of inhibition of glycogenolysis in rat liver by the dihydropyridine derivative, BAY R3401: inhibition and inactivation of glycogen phosphorylase by an activated metabolite.

“…We also assessed levels of G6P, a potential corollary of changes in glycogenolysis, and an effec-DIABETES, VOL. 49 tor in the reciprocal activation of glycogen synthase subsequent to the inactivation of glycogen phosphorylase. Materials.…”

“…When 125 µmol/l BAY R3401 was added, the rate of glycogenolysis dropped precipitously and then slowly declined further during the next 30 min. In the intact liver, glycogenolysis is exclusively catalyzed by phosphorylase a (30,49). The drop in glycogenolytic output (to 17 ± 1% of preinhibitor rates, n = 5) could be explained in part by a drop in phosphorylase a levels (to 37 ± 4% of preinhibitor levels) (Fig.…”

The cytosolic concentration of phosphate determines the maximal rate of glycogenolysis in perfused rat liver

“…A linear, correlation between the maximal glycogenolytic rate and the hepatic Pi signal would indicate that the Km of phosphorylase a for Pi is well above the Pi concentrations that occur in the cytosol, even during hypoxia. DISCUSSION Anoxia and metabolite control of phosphorylase activity A number of manipulations are known to induce enhanced hepatic glycogenolysis (Vandebroeck et al, 1985(Vandebroeck et al, , 1988. These include anoxia, or functional equivalents thereof, such as the administration of mitochondrial poisons.…”

“…In the liver, glycogenolysis is exclusively catalysed by the phosphorylated a form of glycogen phosphorylase (Vandebroeck et al, 1985(Vandebroeck et al, , 1988. Reported Km values of the enzyme in vitro for its substrate, Pi, range from as low as 1 mm (Van den Berghe et al, 1973) to as high as 20 mm, depending on the anionic composition of the medium (Stalmans & Gevers, 1981).…”