Dinitrocresol and Phosphate Stimulation of the Oxygen Consumption of a Cell-free Oxidative System Obtained from Sea Urchin Eggs By

Various substituted phenols have been found to produce, in low concentrations, a two to three hundred per cent increase in the oxygen consumption of sea urchin eggs. As the concentration of a given substituted phenol is increased, the rate of oxygen consumption passes through an optimum and then declines to or below the normal rate. At concentrations larger than that for optimum oxygen consumption these agents produce a reversible block to the cell division of the fertilized eggs (1-3). The mechanism of the two phases of the substituted phenol action, namely, the stimulation of oxygen consumption on the one hand and the inhibition of oxygen consumption and reversible block to cell division on the other hand, has received intensive study over the past several years. The analysis of the first phase of the effect has been hampered by the fact that the oxidative stimulation has been obtainable only with intact cells. Efforts to account for the second phase of the effect have revealed that the substituted phenols, when used at adequate concentrations, inhibit the following enzyme systems and cellular activities: d-amino acid oxidase (a flavoprotein) (4), Zwischenferment and cytochrome reductase (5), growth (6), and phosphate uptake by yeast cells (7), nitrogen assimilation (8), formation of adaptive enzymes (9), and certain other synthetic reactions (10). Recently, Loomis and Lipmann (11), using a cell-free kidney granule preparation of the type previously employed by Green, Loomis, and Auerbach (12), have reported observations which bear on both phases of the substituted phenol effect. They found that 2,4-dinitrophenol at a concentration of 8 X 10 --~ substantially increased the oxygen consumption of this cell-free preparation. However, when the 2,4-dinitrophenol was used at a higher concentration, 1.8 X 10 -4 M, the oxygen consumption was reduced to a normal level and inhibition of aerobic phosphorylation was observed. This observation was of especial interest in its bearing on the mechanism of action of substituted phenols for two reasons: first, it was the first case in which a stimulation of oxygen consumption in a cell-free system had been obtained by the use of substituted phenols; and, second, the inhibition of phosphorylation associated with a decrease in oxygen consumption may provide an explanation for the above mentioned inhibition of oxidative synthetic reactions which are dependent, directly or indirectly, on aerobic phosphorylation (13). 503