The first glycine metabolic pool in man

Abstract

The dilution which orally administered isotopically labeled glycine undergoes immediately after absorption and distribution was investigated in man. The "pool" of glycine with which the labeled amino acid becomes diluted under these curcumstances is termed the "first glycine metabolic pool". Free urinary glycine (isolated as the 2,4-dinitrophenyl derivative) was used as a sample of the first glycine metabolic pool. In experiments with [1-C13] glycine and [N15] glycine 3 hr. urine collections yield sufficient material for mass-spectrpmetric analysis. The rate of change in the isotope content of the first glycine metabolic pool after a single oral dose of isotopically labelled glycine can be represented as the sum of 2 exponential functions. The first glycine metabolic-pool size and turnover rate of a 72 kg adult were of the order of 5.8 g (1.07 mmole/kg body wt} and 3.2 g/hr. (0.59 mmole/kg body/hr.), respectively. The isotope content of urinary hippurate and of the first glycine metabolic pool were compared during a period when repeated doses of isotopically labeled glycine were being given and after a single oral dose of the labeled amino acid. The isotope content of the glycine moiety of the urinary hippuric acid, even in the absence of loading doses of benzoate, does not indicate the isotope content of the first glycine metabolic pool during or shortly after the administration of labeled amino acid, although it may do so later.