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Glycine and serine are interconverted by serine hydroxymethyltransferase and hence share their metabolic pathways. In the rat the carbon skeleton of choline is derived from the alpha and beta carbons of serine through phosphatidylserine and is further converted to that of glycine through N-methylated molecules of glycine i.e. betaine, N-dimethylglycine, and sarcosine (N-methylglycine). Thus far, the production of a folate derivative of the active one carbon that is an essential material for purine nucleotides and thymidylate biosynthesis is the notable feature of this metabolic process. In the major degradative pathway for pyrimidine nucleotides, beta-alanine, one of omega-amino acids, is produced and further catabolized by beta-alanine: oxoglutarate transaminase which is suggested to be identical to that for gamma-aminobutyrate, another omega-amino acid. Disorders included in these metabolic pathways are succinctly reviewed.

5-Fluorouracil (5-FU) metabolism on tumors was studied by in-vivo 19F-MRS (magnetic resonance spectroscopy). In this study, two kinds of tumors were used, i.e., Yoshida sarcoma implanted subcutaneously to the abdomen of rats and drug-induced tumors in the rats livers. Sequential 19F spectra were obtained just after 150 mg/kg 5-FU injected intravenously. In Yoshida sarcoma, the accumulation of 5-FU was observed and disappearance of 5-FU was slower compared to the normal tissue. However, synthesis of fluoronucleotides (Fnct) could not be detected. In drug-induced liver tumors, the peak of fluoro-beta-alanine (FBAL) was observed. Disappearance of 5-FU and catabolism to FBAL in the liver tumors group were slower compared to the normal liver. Synthesis of Fnct did not increase in the liver tumor group. The results in the liver tumor group are considered to be the confined result of the hepatocytes and tumors cells. It was considered that the delayed catabolism to FBAL in the liver tumor group showed metabolic dysfunction of the liver. Also the synthesis of Fnct in tumors could not be detected by in-vivo 19F-MRS. 19F-MRS method could not detect Fnct in tumors in-vivo. However, the accumulation of 5-FU could be assessed by this method. It is expected that the evaluation of 5-FU pooling in tumors could be used for the index of chemotherapeutic effect.

Using microvillous membrane vesicles prepared from human full term placenta, we studied the placental beta-amino acid transport mechanism. The transport of amino acids into microvillous membrane vesicles was studied by a filtration technique using a millipore filter. The uptake of beta-alanine into microvillous membrane vesicles was dependent on Na+ electrochemical gradient (extravesicular greater than intravesicular). The initial rate of this Na+ gradient dependent beta-alanine transport exhibited saturation kinetics with respect to the beta-alanine concentration: an apparent Km of 0.24 mM and Vmax of 46 pmol/mg protein/20 sec were calculated. Taurine inhibited beta-alanine uptake into microvillous membrane vesicles, but on the other hand L-alanine didn't inhibit this beta-alanine uptake. The L-alanine uptake into microvillous membrane vesicles was Na+ electrochemical gradient dependent and the initial rate of this Na+ dependent L-alanine uptake into vesicles was faster than the uptake of Na+ itself into vesicles. On the other hand, the initial rate of Na+ dependent beta-alanine and taurine uptake into vesicles was slower than the uptake of Na+ itself into vesicles. These results indicated that there existed a beta-amino acid specific transport system in human placental microvillous membrane, and placental taurine transport was carried out by this system. And it was also indicated that this placental beta-amino acid transport mechanism is quite different from that of L-alanine.