DEVELOPMENTAL-CHANGES IN PURINE PHOSPHORIBOSYLTRANSFERASES IN HUMAN AND RAT TISSUES

The hypoxanthine/guanine and adenine phosphoribosyltransferase [EC 2.4.2.8] activities in a wide variety of human tissues were studied during their growth and development from fetal life onward. A wide range of activities develop after birth, with especially high values in the CNS and testes. Postnatal development of hypoxanthine/guanine phosphoribosyltransferase was also defined in the rat. Although there were increases in the CNS and testes, there was also a rise in activity in the liver, which was less marked in man. A sensitive radiochemical assay method, using dTTP to inhibit 5''-nucleotidase activity, suitable for tissue extracts, was developed. No definite evidence of the existence of tissue-specific isoenzymes of hypoxanthine/guanine or adenine phosphoribosyltransferase was found. Hypoxanthine/guanine phosphoribosyltransferase in testes, had a significantly different thermal-denaturation rate constant. The findings are discussed in an attempt to relate activity of hypoxanthine/guanine phosphoribosyltransferase to biological function. Growth as well as some developmental changes appear to be related to increases in the activity of this enzyme.