Phenylglyoxal inhibition of the mitochondrial FF-ATPase activated by Mg or by Ca provides clues on the mitochondrial permeability transition pore.

Phenylglyoxal (PGO), known to cause post-translational modifications of Arg residues, was used to highlight the role of arginine residues of the FF-ATPase, which may be crucial to yield the mitochondrial permeability transition pore (mPTP). In swine heart mitochondria PGO inhibits ATP hydrolysis by the FF-ATPase either sustained by the natural cofactor Mg or by Ca by a similar uncompetitive inhibition mechanism, namely the tertiary complex (ESI) only forms when the ATP substrate is already bound to the enzyme, and with similar strength, as shown by the similar K'i values (0.82 ± 0.07 mM in presence of Mg and 0.64 ± 0.05 mM in the presence of Ca). Multiple inhibitor analysis indicates that features of the F catalytic sites and/or the F proton binding sites are apparently unaffected by PGO. However, PGO and F or F inhibitors can bind the enzyme combine simultaneously. However they mutually hinder to bind the Mg-activated FF-ATPase, whereas they do not mutually exclude to bind the Ca-activated FF-ATPase. The putative formation of PGO-arginine adducts, and the consequent spatial rearrangement in the enzyme structure, inhibits the FF-ATPase activity but, as shown by the calcium retention capacity evaluation in intact mitochondria, apparently favours the mPTP formation.