Absorption of the natural purines and pyrimidines by the gut of the chiton, Cryptochiton stelleri

The everted sac technique was utilized to study the absorption of three pyrimidines (thymine, uracil, and cytosine) and four purines (guanine, hypoxanthine, adenine, and uric acid) in the gut of the primitive mollusc Cryptochiton stelleri. Thymine was shown to be actively transported in a concentration range of 0.156-15.60 nM/ml. Saturation kinetics were not observed at the highest concentration of thymine used. Thymine and guanine were actively transported in all regions of the chiton gut tested. Uracil was actively transported only in the proximal anterior gut, whereas hypoxanthine was actively transported only in the posterior gut regions. Cytosine, adenine, and uric acid displayed only fractional S/M ratios and negative net serosal accumulation values which indicated that these purines and pyrimidines were not actively transported. Studies using anaerobic conditions or DNP indicated that the active transport mechanism for the purines and pyrimidines in the chiton gut was dependent on a constant supply of metabolic energy. [...]