Phosphate transport in rat liver mitochondria: Location of sulfhydryl groups essential for transport activities

Abstract

The membrane orientation and symmetry of protein thiol group(s) necessary for transport of Pi in rat liver mitochondria have been assessed by comparing inhibition of transport in intact mitochondria to that in inverted vesicles of purified inner membrane. The permeability characteristics of a variety of inhibitors have been determined under specified conditions. The sensitivities of the uptake pathways in mitochondria and in inverted vesicles appear thus far to be identical. By comparing results with permeant and nonpermeant inhibitors, or sequential treatment with different inhibitors, arguments can be made in favor of a single reorienting site of thiol sensitivity.

Phosphate transport processes in eukaryotic cells

“…The (ADN) exchanger is sensitive to NEM under certain conditions, but not to mercurials (Aquila, Eiermann & Klingenberg, 1982a). Some sulfhydryl reagents such as 5,5'-dithiobis (2-nitrobenzoate), mersalyl, and diazobenzenesulfonate (Wehrle & Pedersen, 1981;Fonyo & Vignais, 1980) and eosin-5-maleimide (Houstek & Pedersen, 1985) inhibit Pi transport under conditions in which they have been rigorously shown not to enter the mitochondrion. Griffiths et aI.…”

Characterization of phosphate efflux pathways in rat liver mitochondria

“…It is possible that the inhibitor-insensitive P1 effiux pathway may correspond to a fraction of P,/H+ carrier molecules in a conformation unreactive toward thiol-specific reagents. Alternatively, a separate P1 effiux carrier may exist (Wehrle et al, 1978;Wehrle & Pedersen, 1981). Further experiments are required to distinguish more clearly the P, influx and efflux pathways at the molecular level.…”

“…carrier is required for the efflux pathway (Azzone et al, 1976; 1978; Wehrle & Pedersen, 1981). This uncertainty has arisen from two types of evidence.…”

“…) (Siliprandi et al, 1975;Azzone et al, 1976; Reynafarje & Lehninger, 1978;Fonyo & Vignais, 1979;Tyler, 1980). Secondly, studies with intact mitochondria and purified inverted inner-membrane vesicles indicate that the energy-coupling mechanisms involved may differ depending on the direction of phosphate transport (Coty & Pedersen, 1974;Wehrle et al, 1978;Wehrle & Pedersen, 1981).…”

Tl+ Showed Negligible Interaction with Inner Membrane Sulfhydryl Groups of Rat Liver Mitochondria, but Formed Complexes with Matrix Proteins

“…The amount of mitochondrial sulfhydryl groups (MSG) ranges from 85 to 100 nmol/g of protein . These groups are necessary in oxidative phosphorylation processes, adenine nucleotide translocation, succinate dehydrogenation , and phosphate cotransportation . The oxidation of SH groups in the inner mitochondrial membrane (IMM) facilitates opening of the mitochondrial permeability transition pore (MPTP) .…”