title: Inhibition of pyruvate kinase activity by cystine in brain cortex of rats.
abstract: Cystinosis is a metabolic disturb associated with excessive lysosomal cystine accumulation secondary to defective cystine efflux. Patients affected by this disease develop a variable degree of symptoms depending of the involved tissues. Accumulation of cystine in the brain may lead to severe neurological symptoms. However, the mechanisms by which cystine is neurotoxic are not fully understood. Considering that pyruvate kinase (PK) is a thiolic enzyme crucial for the glycolytic pathway, and disulfides like cystine may alter thiolic enzymes by thiol/disulfide exchange, the main objective of the present study was to investigate the effect of cystine on PK activity in the brain cortex of developing Wistar rats. We also performed kinetic studies and investigated the effects of GSH, a biologically occurring thiol groups protector, and cysteamine (CysN), the drug used for cystinosis treatment, on the enzyme activity. We observed that cystine inhibited the enzyme activity by two different mechanisms, one through the competition with ADP and phosphoenolpyruvate (PEP), and the other non-competitively, probably through oxidation of the thiol groups of PK. We also observed that GSH and cysteamine fully prevented and reversed the inhibition caused by cystine. Considering that cysteamine is used in patients with cystinosis because it causes parenkimal organ cystine depletion, the present data provides a possible new beneficial effect for the use of this drug.
authors.affiliation: Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, UFRGS, Rua Ramiro Barcelos 2600, CEP 90.035-003, Porto Alegre, RS, Brazil.
authors.forename: Luciane Rosa
authors.initials: LR
authors.lastname: Feksa
authors.forename: Andrea
authors.initials: A
authors.lastname: Cornelio
authors.forename: Carlos Severo
authors.initials: CS
authors.lastname: Dutra-Filho
authors.forename: Angela Terezinha
authors.initials: AT
authors.lastname: De Souza Wyse
authors.forename: Moacir
authors.initials: M
authors.lastname: Wajner
authors.forename: Clovis Milton Duval
authors.initials: CM
authors.lastname: Wannmacher
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects* / Q000201:enzymology*; D003553:Cystine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D011770:Pyruvate Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D004791:Enzyme Inhibitors; D003553:Cystine; D011770:Pyruvate Kinase