Inhibition of select mitochondrial enzymes in PC12 cells exposed to S-(1,1,2,2-tetrafluoroethyl)-L-cysteine.
Many halogenated foreign compounds are detoxified by conversion to the corresponding cysteine S-conjugate, which is N-acetylated and excreted. However, several halogenated cysteine S-conjugates [e.g. S-(1,1,2,2-tetrafluoroethy)-L-cysteine (TFEC)] are converted to mitochondrial toxicants by cysteine S-conjugate beta-lyases. In the present work, we showed that TFEC appreciably inactivated highly purified alpha-ketoglutarate dehydrogenase complex (KGDHC) in the presence of a cysteine S-conjugate beta-lyase. Incubation of PC12 cells (which contain endogenous cysteine S-conjugate beta-lyase activity) with TFEC led to a concentration- and time-dependent loss of endogenous KGDHC activity. A 24-hr exposure to 1 mM TFEC decreased KGDHC activity in the cells by 90%. Although treatment with TFEC did not inhibit intrinsic pyruvate dehydrogenase complex (PDHC) activity, it inhibited dichloroacetate/Mg2+-mediated activation/dephosphorylation of PDHC in the PC12 cells by 90%. To determine the selectivity of enzymes targeted by TFEC, several cytosolic and mitochondrial enzymes involved in energy metabolism [malate dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase, glutamate dehydrogenase, lactate dehydrogenase, cytosolic and mitochondrial aspartate aminotransferases (AspAT)] were also assayed in the PC12 cells exposed to 1 mM TFEC for 24 hr. Of these enzymes, only mitochondrial AspAT, a key enzyme of the malate-aspartate shuttle, was inhibited. The present results demonstrate a selective vulnerability of mitochondrial enzymes to toxic cysteine S-conjugates. The data indicate that TFEC may be a useful cellular/mitochondrial toxicant for elucidating the consequences of the diminished mitochondrial function that accompanies numerous neurodegenerative diseases.
Park
L C
LC
Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY, USA.
Gibson
G E
GE
Bunik
V
V
Cooper
A J
AJ
D000818:Animals; D013437:Carbon-Sulfur Lyases / Q000378:metabolism; D003545:Cysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000201:enzymology; D016716:PC12 Cells; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D051381:Rats; D000637:Transaminases / Q000378:metabolism; D005466:Fluorocarbons
D013437:Carbon-Sulfur Lyases; D003545:Cysteine; D004791:Enzyme Inhibitors; D006845:Hydrocarbons, Fluorinated; D007655:Ketoglutarate Dehydrogenase Complex; D011768:Pyruvate Dehydrogenase Complex; D000637:Transaminases; C064116:S-(1,1,2,2-tetrafluoroethyl)cysteine; D005466:Fluorocarbons; C020656:glutamine-pyruvate aminotransferase; C108902:cysteine-S-conjugate beta-lyase