[The effect of fluoride ion on the activity of succinate dehydrogenase isolated from the pig's renal cortex].

Succinate dehydrogenase is a membrane-bound mitochondrial enzyme providing the respiratory chain with electrons. In natural environment the enzyme is a part of the respiratory chain and slight changes in the content of phospholipids (during preparation) qualify the enzyme to ubiqinone reductase titer. The actual paper answers the question of how major, selected inorganic anions metabolically influence succinate dehydrogenase. The objective of the paper was to determine: 1) what influence on SDH activity is exerted by ionic strength; 2) how do fluoride, phosphate and chloride influence the activity of succinate dehydrogenase present in submitochondrial particles. Mitochondria were prepared on the basis of King's method. Mitochondria and submitochondrial particles were obtained from mitochondria isolated from the pig's kidney. The activity of enzyme was measured by polarographic method with the aid of phenasine methosulphate and dichloroindophenol. The protein concentration was determined by the Gornal's method. The following conclusions have been drawn, namely: The activity of enzyme is not modified by means of ionic strength (Fig. 1, 2, 3). Fluoride exerts influence on the enzyme as a competitive inhibition when the concentration of succinate in the sample is of the order 1 x 10(-3), 5 x 10(-4), 2 x 10(-4) mol/dm3, with concentrations of succinate higher than 2 x 10(-2), 2 x 10 mol/dm3 the fluoride ion behaves as a typical non-competitive inhibitor (Fig. 4). Phosphates modified the activity of enzyme, and exerted influence as its competitive inhibitor (Fig. 5, 6). In the process of SDH inhibition induced by fluoride ion there are two separately acting mechanisms which respectively involve one or two ions. As it has been found out their effect also depends on the amount of succinate in the environment. The first mechanism appears in condition of high succinate concentration in the solution (about 20 mmol/dm3), when the active centre of enzyme is completely saturated by the substrate. The by fluoride induced inhibition is of non-competitive character, which means that single F ion binds to enzyme outside its active centre (which is occupied by substrate). On the other hand, when the concentration of succinate is close to 1 mmol/dm3, under conditions of incomplete saturation of the active centre by substrate, the enzyme is being inhibited competitively, and, as indicated, 2 fluoride ions bind with it (Fig. 7, 8).