The absorption of amino acids across the guts of chitons and sea cucumbers

The movement of six amino acids across the guts of two marine invertebrates Stichopus parvimensis and Cryptochiton stelleri was studied. The everted sac preparation of Crane and Wilson (1958) was used to study the movement of labeled glycine, alanine, AIBA, proline, glutamic acid and lysine. Positive S/M ratios were obtained when alanine and glycine were tested in S. parvimensis gut segments indicating probable active transport of these two amino acids. Fractional S/M ratios were obtained when AIBA, proline, glutamic acid and lysine were used as substrates. These fractional ratios were interpreted as evidence against the occurrence of active transport of these amino acids by holothurian gut. Alanine, glycine, AIBA, proline and lysine were accumulated against a concentration gradient by the mid and distal posterior segments of C. stelleri gut. Lysine was accumulated by the proximal, mid, and distal posterior segments. Alanine was also concentrated by the anterior gut of this animal. There was no accumulation of glutamic acid by any region tested. The chiton amino acid active transport system was shown to be dependent on aerobic energy. Placing the preparations under nitrogen reduced the amount of alanine, proline, AIBA, glycine and lysine transported. The inhibition was reversible as demonstrated by returning the previously inhibited preparations to the aerobic state. The chiton active transport mechanism was temperature sensitive. Greater S/M ratios were obtained for glycine, AIBA, proline and lysine at 15 C than at 5 C. Raising the temperature to 25 C produced a reduction in S/M ratios for all five of the amino acids tested. An increase in S/M ratios was also observed as the temperature was raised from 10 C to 20 C. When the temperature was reduced from 20 C to 10 C, the S/M values decreased accordingly. Q10 values were calculated for the temperature studies, and these values were consistent with the values of known active transport processes.