High-performance liquid chromatography was used to measure the simultaneous transport of 16 amino acids from seawater into the mussel Mytilus edulis. All the substrates, including representative neutral, basic, and acidic amino acids, were accumulated from ambient concentrations as low as 5 nM. Influx of four radioactively labeled amino acids was compared with their net flux. In each case the influx of the 14C-labeled substrate, determined from the removal of isotope from test solutions, accurately represented the net flux of that substrate as measured by direct chemical analysis. Ammonia was the only compound observed to be routinely lost from these animals. Rates of uptake of individual amino acids, each at concentrations of 10 nM, ranged from 2.4 to 7.0 nmol . g dry flesh wt-1 . min-1. The studies show that M. edulis is capable of a net uptake of dissolved amino acid from the very low concentrations characteristic of seawater. Moreover, net accumulation can occur against chemical gradients calculated to be in excess of one million to one. The rates of amino acid uptake may contribute significantly to the animals' energy requirements.
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