[Action of a new compound, derived from NEM and DTE, on anionic translocation in mitochondria]

The activity of translocating system which mediates the transport of Pi and citric cycle intermediates in mitochondria, has been determined with the multi-layer centrifugation technique. Contrary to all expectation it has been found that NEM, which binds tightly to SH groups, and DTE which reacting with disulphides increases the number of thiol groups of mitochondrial membrane, both inhibited the Pi leads to OH- and increased the initial rate of succinate leads to Pi exchange diffusion reactions. Identical results were obtained when mitochondria were preincubated with both NEM and DTE. The possibility that in these last conditions the effect on the translocator could be not determined by NEM and DTE per se but by a compound derived from their interaction, has been tested. Indeed solutions of NEM and DTE added in the concentration ratio of 2 to 1 and in absence of mitochondria, promoted the formation of a new compound, indicated as DTS, evidentiable by following the disappearance of both the absorbance of NEM at 302 nm and the free SH groups of DTE. Succinate leads to Pi and Pi leads to OH- exchange reactions were respectively stimulated and inhibited by DTS with a behaviour comparable to that observed in presence of NEM and/or DTE. The results are interpreted as a further and decisive support to the hypothesis that SH groups cannot be considered as functional active sites of the translocating system.