THE PURINES AND PURINE METABOLISM OF SOME TUMORS IN DOMESTIC ANIMALS

The purines of tumors are generally the same as those of the normal tissue, chiefly guanine and adenine, little more than traces of xanthine, and relatively small amounts of hypoxanthine being found. No uric acid was found in the tumors of this series. In one tumor, an embryonal adenosarcoma in a pig's kidney, a large amount of hypoxanthine, and no adenine was found, while the yield of xanthine was also unusually high. This result cannot be explained at present on experimental grounds, but evidently a nucleic acid complex containing no adenine was encountered. Possibly hypoxanthine was present in inosinic acid. The purine enzymes are generally the same in tumors as in the normal tissue from which the tumors are derived. This fact sometimes makes it possible to learn by chemical study from what tissue a given kind of tumor is derived, when the microscopic evidence is inconclusive. Although the liver of the sheep contains the enzyme xanthine oxidase, it may be absent from primary tumors in the sheep liver, as it has also been shown to be from secondary tumors in the human liver. As xanthine oxidase is one of the last of the purine enzymes to develop in the embryonal organism, its absence in a malignant tumor containing otherwise the same purine enzymes as the tissue from which it is derived, is evidence of the embryonal character of the tumor tissue.