Glyconeogenic pathway in isolated skeletal muscles of rats.
Although the conversion of lactate to glycogen (glyconeogenesis) in muscle was demonstrated a long time ago, the biochemical reactions responsible for this process are still a controversial matter. In the present study, advantage was taken from the specific inhibition induced by phenylalanine on muscle pyruvate kinase (PK) to investigate the role of reverse PK activity in muscle glyconeogenesis. Addition of phenylalanine to the incubation medium of a preparation of isolated, intact skeletal muscles that maintain metabolic activity for several hours reduced by 50% the rate of incorporation of [14C]lactate or [14C]bicarbonate into muscle glycogen. Muscle extracts presented high levels of maximal activity of PK in the reverse direction, which was completely blocked in the presence of phenylalanine. In contrast, mercaptopicolinic acid, an inhibitor of phosphoenolpyruvate carboxykinase (PEPCK), did not affect the incorporation of 14C from either lactate or bicarbonate into muscle glycogen. Maximal PEPCK activity was much lower in muscle extracts than in gluconeogenic or glyceroneogenic tissues and was suppressed in the presence of mercaptopicolinic acid. The data suggest that a reversal of the metabolic flux through the reaction catalyzed by PK contributes to the accumulation of lactate-derived glycogen that occurs in skeletal muscle under certain physiological conditions.
Xavier
Analúcia Rampazzo
AR
Department of Biochemistry, Immunology and Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil.
Roselino
José Eduardo de Salles
JE
Resano
Neusa Maria Zanon
NM
Garófalo
Maria Antonieta Rissato
MA
Migliorini
Renato Helios
RH
Kettelhut
Isis do Carmo
Ido C
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D002250:Carbon Radioisotopes; D006597:Fructose-Bisphosphatase / Q000378:metabolism; D006003:Glycogen / Q000096:biosynthesis*; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism* / Q000494:pharmacology; D008291:Malate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010649:Phenylalanine / Q000494:pharmacology; D010848:Picolinic Acids / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D001639:Bicarbonates; D002250:Carbon Radioisotopes; D010848:Picolinic Acids; D019344:Lactic Acid; D010649:Phenylalanine; D006003:Glycogen; D007770:L-Lactate Dehydrogenase; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); C069767:phosphoenolpyruvate carboxylase kinase; D011770:Pyruvate Kinase; D017346:Protein Serine-Threonine Kinases; D006597:Fructose-Bisphosphatase