Dinitrocresol and phosphate stimulation of the oxygen consumption of a cell-free oxidative system obtained from sea urchin eggs

Action of nitro- and halophenols upon oxygen consumption and phosphorylation by a cell-free particulate system from arbacia eggs

1. The ability of 4,6-dinitrocresol and eight other substituted phenols to stimulate oxygen uptake and inhibit phosphorylation by a cell-free particulate system from unfertilized Arbacia eggs has been determined. Five of those agents can produce both stimulation of oxygen consumption and inhibition of phosphorylation; one inhibits both oxygen consumption and phosphorylation; and two have no effect on either oxygen consumption or phosphorylation. In every case the effects of these substituted phenols upon the cell-free particulate systems parallel those upon oxygen consumption and cleavage in the intact fertilized Arbacia eggs. 2. The data suggest that energy for cleavage of the Arbacia egg is provided at least in part by oxidative phosphorylation and that substituted phenols may block cleavage by interfering with generation and transfer of high-energy phosphate groups.

Oxidative phosphorylation by a cell-free particulate system from unfertilized arbacia eggs

1. A cell-free particulate system capable of effecting oxidative phosphorylation has been prepared from unfertilized eggs of Arbacia punctulata. A substantial increase in phosphorylation can be produced by addition of alpha-ketoglutarate, oxalacetate, or succinate, the magnitude of the increase being greatest with alpha-ketoglutarate. The activity of the phosphorylating system is sharply dependent on maintenance of a comparatively narrow pH range during both the preparation of the particulate system and its subsequent incubation with oxidizable substrate. 2. The maximum oxygen consumption of the cell-free particulate system derived from a given weight of unfertilized eggs is about three times that of the same weight of intact unfertilized eggs and approximately the same as that of an equal weight of fertilized eggs. 3. The data indicate that generation of high-energy phosphate bonds in the Arbacia egg is coupled, as it is in mammalian liver or kidney, with the functioning of the tricarboxylic acid cycle.

Regulation of the tricarboxylic acid cycle in sea urchin eggs and embryos

Contents of the tricarboxylic acid (TCA) cycle intermediates, coenzyme A (CoA) derivatives, and carnitine derivatives were estimated in the developing eggs and embryos of the sea urchin, Anthocidaris crassispina. Levels of the TCA cycle intermediates in unfertilized eggs were similar. The level of malate increased remarkably after fertilization and reached a plateau just before hatching out. Slight elevation in the level of citrate was also observed during early development. These suggest that metabolism of citrate and malate is altered during development. Long-chain fatty acyl-CoA was accumulated in unfertilized eggs. Its level decreased after fertilization, then gradually increased until the late gastrula stage and turned to decline. Free CoA level increased after fertilization and reached a peak around the gastrula stage, and thereafter it decreased, while short-chain acyl-CoA level decreased gradually after fertilization. Crude citrate synthase from sea urchin unfertilized and fertilized eggs was inhibited by palmitoyl-CoA, though malate dehydrogenase was not inhibited. The palmitoyl-CoA-caused inhibition of citrate synthase was also relieved by spermine and spermidine. In view of the inhibition of citrate synthase by palmitoyl-CoA at concentrations in unfertilized eggs, the enzyme is probably inhibited in unfertilized eggs by long-chain acyl-CoA and released from the inhibited state by the decrease in the level of long-chain acyl-CoA and the increase in the level of polyamines following fertilization.