Net uptake rates by Glycera dibranchiata Ehlers of 18 amino acids, each present in artificial sea water at an initial concentration of 1 μmol l−1, were estimated using high-performance liquid chromatography (HPLC). Uptake rates for 14C-labelled alanine, arginine, aspartate, glutamate, glycine and serine, presented singly at an initial concentration of lμmol l−1, were estimated by observing disappearance of radioactivity from the ambient solution. Net entry of alanine, arginine, aspartate and serine was estimated by HPLC in parallel samples of the medium. There was no significant difference in the rate of influx of labelled substrate and net entry estimated by HPLC for these amino acids. Ligature of the anterior and posterior ends of the worms did not perceptibly modify rates of uptake. Distribution of radioactivity to the internal and external body wall, coelomocytes, gut and coelomic fluid was observed after 1 h of incubation in lμmol l−1 serine. Rates of exchange of labelled carbon were estimated for all combinations of these internal tissues by taking advantage of morphological features of Glycera. Amino acid pools in each of the tissues of the worms are described, based on HPLC analyses. Internal distribution of radioactivity derived from [14C]serine is compared with total pools based on estimates of tissue volume and the normal serine content of free amino acid pools for each tissue. The distribution of the non-metabolized analogue cycloleucine is also described at the end of 1 h of incubation.

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