Characterization of the inhibition of pyruvate kinase caused by phenylalanine and phenylpyruvate in rat brain cortex.
Pyruvate kinase plays a crucial role on the glycolytic pathway, the main route that provides energy for brain functioning. In the present study, we investigated the kinetics of the inhibition of pyruvate kinase provoked by phenylalanine and its main metabolite, phenylpyruvate, in mitochondria-free cerebral cortex homogenate from 22-day-old Wistar rats. We found that phenylalanine and phenylpyruvate inhibit PK activity by competition with the enzyme substrates ADP and phosphoenolpyruvate. We also investigated the interaction between phenylalanine and phenylpyruvate, and the kinetics of alanine prevention of the inhibitory action of phenylalanine and phenylpyruvate on pyruvate kinase activity. We observed that alanine per se had no effect on PK activity but prevented the inhibitory action of phenylalanine and phenylpyruvate by competition. The data suggest that phenylalanine, phenylpyruvate, and alanine act on a common site in the enzyme, probably an allosteric one. It is possible that inhibition of brain PK activity may be related to the reduction of glucose metabolism observed in the brain of phenylketonuric patients and may be one of the mechanisms responsible for the neurological dysfunction found in these patients. Further studies, however, are necessary to evaluate the benefit of carbohydrate and alanine supplementation to the diet of phenylketonuric patients.
Feksa
Luciane Rosa
LR
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Rua Ramiro Barcelos 2600, CEP 90.035-003, Porto Alegre, RS, Brazil.
Cornelio
Andrea Renata
AR
Dutra-Filho
Carlos Severo
CS
de Souza Wyse
Angela Terezinha
AT
Wajner
Moacir
M
Wannmacher
Clóvis Milton Duval
CM
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000409:Alanine / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D002540:Cerebral Cortex / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D066298:In Vitro Techniques; D009433:Neural Inhibition / Q000187:drug effects*; D010649:Phenylalanine / Q000494:pharmacology*; D010667:Phenylpyruvic Acids / Q000494:pharmacology*; D010728:Phosphoenolpyruvate / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D010667:Phenylpyruvic Acids; D010649:Phenylalanine; D000244:Adenosine Diphosphate; D010728:Phosphoenolpyruvate; D011770:Pyruvate Kinase; D000409:Alanine; C031606:phenylpyruvic acid