{'fraction_non_alphanumeric': 0.026494565217391304, 'fraction_numerical': 0.002717391304347826, 'mean_word_length': 5.294871794871795, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Ontogeny of Amino Acid Metabolism in Mammalian Kidney

Mammalian kidney transports imino-acids and glycine at physiological concentrations on three t ypes of membrane sites: a low-Km proline system, a low-Km glycine system and a ‘common’ high-Km system. Our recent studies (in press) show that absence of the two low-Km systems accounts for postnatal iminoglycinuria in mammals. Further studies with newborn rat kidney reveal additional ontogenetic features. Uptake: The low-Km proline system becomes active 1 week after birth. The low-Km glycine system is not active until the third week, indicating independent genetic contro of these sites. Efflux: Reduced efflux rates explain increased internal accumulation of soluble aminoacids in newborn kidney, at high and low internal concentrations. Efflux rates evolve with age in a manner suggesting that control of this membrane function is segregated from the control of uptake. Catabolism: Rates of oxidation (measured by 14CO2 formation) and conversion of intracellular L-proline and glycine to other soluble metabolites, are lower in newborn kidney compared to mature kidney, while protein incorporation rates are enhanced in the former. These events do not account for the differences between newborn and adult kidney in net transport of substrate. Ontogeny of iminoglycine metabolism in kidney thus involves independent regulation of influx, efflux, incorporation and oxidation. (Supported by grants from MRC, Canada).