Abstract
It is known that the oxygen consumption of fertilized sea urchin eggs (Arbacia punctulata) can be markedly stimulated by the addition of suitable concentrations of nitro and dinitrophenols. 1 , 2 Stimulation of oxygen consumption in these cells can also be effected by certain oxidation-reduction indicators. 5 , 6 In concentrations slightly greater than the optimum for respiration, certain nitrophenols block the cell division of fertilized Arbacia eggs. This division block is fully reversible since the eggs, when returned to sea water after a 3-hour exposure to concentrations many times the optimum for respiration, resume division and develop to swimming larvae. 1 In concentrations which are optimum for respiration, a number of oxidation-reduction indicators also inhibit cell division in fertilized Arbacia eggs, but the eggs so treated do not recover when they are returned to sea water. 5 , 6
Since the chemical and biological properties of the nitro compounds differ in almost every respect from those of the oxidation-reduction indicators, 5 it has been tentatively concluded that the nitro and dinitrophenols do not stimulate respiration or block cell division as a result of any possible oxidation or reduction which they may undergo in the cell. For the production of the respiratory-stimulating and division blocking effects, the unesterified phenolic OH group, accompanied by suitable substituents in the benzene ring, appears essential. 3
The experiments presented here support this view since they show that, in fertilized eggs of Arbacia punctulata, oxygen consumption is stimulated and cell division is reversibly blocked by phenols containing no nitrogen and no substituent group capable of oxidation-reduction. These phenols contain, in addition to the OH group and the benzene ring, only chlorine, bromine, or iodine atoms. Phenols of this type are oxidized irreversibly at high positive potentials. 4
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