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>Phosphate transport in fertilized sea urchin eggs. II. Effects of metabolic inhibitors and studies on differentiation
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Phosphate transport in fertilized sea urchin eggs. II. Effects of metabolic inhibitors and studies on differentiation
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机译：Phosphate transport in fertilized sea urchin eggs. II. Effects of metabolic inhibitors and studies on differentiation
AbstractMetabolic inhibitors were applied after the transport system was fully developed in concentrations sufficient to block cleavage. 0.5–1.0 × 10−4M cyanide and anaerobiosis caused from negligible to moderate (40%) inhibition of phosphate uptake. The inhibition occurred late in the breeding season, and the inhibitory action of cyanide on uptake was associated with irreversible developmental effects. Azide (3 × 10−3M) did not inhibit uptake when the chamber method was used, but the aliquot and Hopkins' tube methods gave considerable inhibition. Purified preparations of 2,4‐dinitrophenol (1 × 10−4M) did not inhibit uptake. Sodium iodoacetate (up to 0.05 M) and phlorizin (0.005 M) exerted no effect.Calculations of the minimal work requirement for the transport process reveal that this amounts to only a small fraction (0.24% at an external phosphate concentration of 2 μM) of the total available metabolic energy.Exposure of eggs at five minutes after insemination (lag phase) to cyanide (5 × 10−5M), anaerobic conditions, or azide (3 × 10−3M) blocked the expected increase of phosphate uptake. Removal of the inhibitors led to resumption of development and the appearance of the phosphate transport system in an essentially normal pattern.Exposure of eggs to 1.4–2.0 × 10−4M p‐chloromercuribenzoate (p‐CMB) during the accumulation phase severely depressed phosphate uptake, but cleavage was not inhibited nor delayed; recovery from the inhibition was accelerated by 1 × 10−3M cysteine. Exposure to p‐CMB during the lag phase blocked the appearance of the transport system; cleavage proceeded normally. After the removal of p‐CMB little reversal occurred until the addtion of 1 × 10−3M cysteine, when the phosphate transport system developed in an essentially normal manner.Trypsin (0.001–0.01%) neither activates the transport system in unfertilized eggs, nor inactivates it in denuded fertilized eggs by removal of surface proteins.The data are consistent with the conclusion that (1) the phosphate transport system is newly synthesized at fertilization in energy dependent reactions, and (2) phosphate transport is a carrier mediated process no
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