Transport of amino acids by starfish digestive glands

Abstract

1. 1. Isolated starfish digestive glands can take up through their peritoneal surfaces and concentrate fifteen different amino acids, which after 5 hr are still retained in an ethanol-extractable state. 2. 2. Methionine is the most rapidly absorbed amino acid. Alanine, serine and other neutral amino acids are also rapidly transported. The basic and acidic amino acids are less readily taken up than most of the neutral amino acids. 3. 3. The neutral amino acids generally inhibit glycine transport in proportion to their affinities for transport, probably indicating a common mechanism for most of their transport. Methionine and, to a lesser extent, proline are less powerful inhibitors than would be expected from their transport rates, suggesting parallel absorptive mechanisms may also be important. 4. 4. The basic amino acids, especially histidine, have significant inhibitory effects on glycine transport, indicating a probable partial overlap of their transport systems with those of the neural amino acids. 5. 5. The two acidic amino acids appear to enhance glycine transport and possibly may be responsible for synergic stimulation of uptake of mixtures of amino acids.