Glycogen phosphorylase and pyruvate dehydrogenase transformation in white muscle of trout during high-intensity exercise

We examined the regulation of glycogen phosphorylase (Phos) and pyruvate dehydrogenase (PDH) in white muscle of rainbow trout during a continuous bout of high-intensity exercise that led to exhaustion in 52 s. The first 10 s of exercise were supported by creatine phosphate hydrolysis and glycolytic flux from an elevated glycogenolytic flux and yielded a total ATP turnover of 3.7 micromol x g wet tissue(-1) x s(-1). The high glycolytic flux was achieved by a large transformation of Phos into its active form. Exercise performed from 10 s to exhaustion was at a lower ATP turnover rate (0.5 to 1.2 micromol x g wet tissue(-1) x s(-1)) and therefore at a lower power output. The lower ATP turnover was supported primarily by glycolysis and was reduced because of posttransformational inhibition of Phos by glucose 6-phosphate accumulation. During exercise, there was a gradual activation of PDH, which was fully transformed into its active form by 30 s of exercise. Oxidative phosphorylation, from PDH activation, only contributed 2% to the total ATP turnover, and there was no significant activation of lipid oxidation. The time course of PDH activation was closely associated with an increase in estimated mitochondrial redox (NAD(+)-to-NADH concentration ratio), suggesting that O2 was not limiting during high-intensity exercise. Thus anaerobiosis may not be responsible for lactate production in trout white muscle during high-intensity exercise.     

Glycogen metabolism in white and red muscle or normal and diabetic rats. Degradation of glycogen by adrenaline.

The author studied the effect of adrenaline (500 mug/kg s.c.) on the glycogen content of white (extensor digitorum longus -- EDL) and red (soleus -- SOL) muscle of normal and alloxan-diabetic rats. In normal rats, whose nutritional state varied at the time of adrenaline administration (after a 24 hours' fast, fed ad libitum or given 5 g glucose/kg as a 20% solution intragastrically 2 hours before injecting adrenaline), no marked post-adrenaline differences were found between the size of the decrease in the amount of glycogen in white and red muscle. In addition, no significant differences were found between the three groups of animals in glycogen concentration in the EDL (0.3+/-0.05, 0.35+/-0.03 and 0.26+/-0.02 mg/g) or in the SOL, apart from one exception (0.23+/-0.02, 0.2+/-0.01, and 0.51+/-0.03 mg/g), after adrenaline. The glycogen concentration in the white and red muscle of diabetic rats fed ad libitum fell to values similar to those in normal rats after adrenaline (0.32+/-0.05 mg/g in the EDL and 0.18+/-0.02 mg/g in the SOL). These results supoort the view of authors who hold that glycogenolysis is possible without pre-activation of phosphorylase; they also support the idea, expressed by Krebs, of the existence of a reciprocal relationship between phosphorylase activity and the glycogen concentration, according to which glycogen itself may influence its own degradation.     

Glycogen phosphorylase activities in skeletal muscle and heart of genetically dystrophic Syrian hamster.

A simple, rapid and reliable procedure of tissue preparation was devised to estimate glycogen phosphorylase activity in cardiac and skeletal muscle of normal and genetically dystrophic Syrian hamsters of various ages. Total phosphorylase activities of dystrophic skeletal muscle, compared to normal, were reduced. Except for the case of heart from the younger dystrophic animals (45 days old), in which higher phosphorylase activity was noted, hearts from dystrophic hamsters, compared to normal, also showed reduced phosphorylase activities. There were, however, no significances in the ratios of phosphorylase alpha to total phosphorylase between the normal and dystrophic tissues.     

Glycogen phosphorylase of skeletal muscles

A review is given on the affinity modification of pyridoxal phosphate and AMP-binding sites as well as on the chemical modification of essential amino acid residues of phosphorylase (histidine residue of the substrate-binding site and cysteine residue of the coenzyme-binding site). The role of allosteric effectors (AMP and glucose-6-phosphate) and functionally important centers of the protein in conformational transitions of rabbit muscle phosphorylase b is discussed. The kinetic properties of rabbit and bovine muscle phosphorylase are compared. Bovine muscle phosphorylase is shown to be a partly phosphorylated form of the enzyme. Some peculiarities of the pH-dependence of kinetic behaviour of the hybrid form of the bovine muscle enzyme are discussed.