Rate of excretion of N15 after feeding N15-labeled l-aspartic acid in man

1. l-Aspartic acid labeled with N¹⁵ was fed to one human adult and six infants, and the total N and N¹⁵ were determined in the urine from time to time. 2. The N¹⁵ concentration (or isotopic ratio) of urinary N reached its maximum in the adult about 2 hours and in the infants about 4 hours after feeding, then fell off logarithmically. 3. Assuming that the N of aspartic acid readily entered into equilibrium with other N compounds in the pool, the rate of turnover of the N pool was calculated from the rate of fall of the isotopic ratio of urinary N. This rate of turnover of N was about 4 per cent per hour in the adult and 6 to 12 per cent per hour in the infants. 4. The rate of protein synthesis calculated from the rate of turnover of N was 10 mg. N per kilo per hour in the adult and 18 to 27 mg. N per kilo per hour in the infants, with one exception which showed a higher rate of 52 mg. N per kilo per hour. The size of the metabolic pool of N per kilo in non-growing infants was about the same as that in the adult (0.4 to 0.5 gm.) but it was somewhat larger in growing infants (0.5 to 0.8 gm.).     

Relative concentrations of N15 in urinary ammonia N and urea N after feeding N15-labeled compounds

Available data on the isotopic ratio See PDF for Equation of ammonia (r_a) and that of urea (r_u) after a single feeding of glycine, aspartic acid, and ammonium citrate are analyzed. From this analysis the following conclusions are drawn. 1. The isotopic ratio See PDF for Equation of ammonia (r_a) is always higher than that of urea (r_u) in the initial period after a single feeding of isotopic glycine or aspartic acid, but the relation is reversed later. A similar relation probably holds after feeding isotopic ammonia. 2. It is pointed out that the ratio of average r_a to average r_u depends on the time interval for which urine is collected, on the schedule of feeding, and probably also on the amount taken at each feeding. When the amount fed and the feeding schedule are unknown, theoretical interpretation of the ratio of average r_u to average r_u is impossible. 3. At the point of maximum isotopic ratio of urea, it is very probably equal to the isotopic ratio of ammonia. A possible explanation is suggested.     

PDX模型在肿瘤医学中的应用进展

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古生物学和地层学研究的定量化趋势——GBDB数字化科研平台的建设及其意义

自上世纪八十年代末以来,基于数据库和各种定量分析方法的古生物学、地层学、古地理学、古生态学研究逐渐成为当今国际地学研究的前沿和热点.中国的古生物学和地层学数字化科研平台的建设,最早的设计思路始于2001年,于2003年进行了首次尝试,并于2007年整合了多种相关数据资源,正式启动了GeoBiodiversity dat...