Eur. J. Biochem. 110,289-293 (1980) zyxwvutsrq Q by FEBS 1980 Activities of Enzymes Involved in Amino-Acid Metabolism in Developing Rat Placenta Xavier REMESAR, LIuis AROLA, Andreu PALOU, and Maria ALEMANY Fisiologia General, Facultat de Biologia, Universitat de Barcelona, Barcelona-7 (Received March 18, 1980) Aspartate transaminase, alanine transaminase, glutamate dehydrogenase, arginase, serine dehydratase, tyrosine transaminase, glutamine synthetase, glutaminase and adenylate deaminase activities were measured in crude homogenates of 12, 19 and 21-day rat placentae. There is a considerable quantitative importance in enzymes able to produce free ammonia, such as adenylate deaminase and glutamate dehydrogenase, activity that progressively decrease with the age of placenta. The glutamine synthetase and tyrosine transaminase activities increase with age, while serine dehydratase decreases considerably and aspartate and alanine transaminase do not change practically. Arginase shows a maximum at 19, with lower 12 and 21-day activities. No measurable glutaminase activity has been found. The possible implications of the enzymes studied upon the ammonia-producing activity of rat placenta are discussed together with the relative decreasing role of placenta for the overall metabolic activity of the foetus, especially during the last phases of its development. The placenta is the interface through which the embryo first, and then the foetus, receive. the foodstuffs needed for their development at the ex- pense of the maternal organism. The vital cycle of the placenta is related to its size relative to that of the foetus; it initially carries on many metabolic functions that are later taken up by other foetal organs, ending its physiological use with birth, when it is totally discarded. The metabolic functions of the placenta are mani- fold in addition to its main connecting and transporting role. Thus, the enzyme activities found in placenta are considerable, and explain an active glucidic and inter- mediary metabolism [l, 21; however, the amino acid metabolism of the placenta has been only sparsely studied, mainly in relation to transaminases [I - 51 ; but also adenylate deaminase [6] and arginase [2,7] have been isolated and/or studied. Human placental gluconeogenic amino acid oxidation has been also described [8]. The purpose of these studies was to determine the relative importance of several main amino acid zyxwvu Enzymes. Aspartate transaminase (EC 2.6.1.1); alanine trans- aminase (EC 2.6.1.2); tyrosine transaminase (EC 2.6.1.5); serine dehydratase zyxwvutsrqpo (EC 4.2.1.13); arginase (EC 3.5.3.1); glutamine synthetase (EC 6.3.1.2); glutaminase (EC 3.5.1.2); adenylate dearninasc (EC 3.5.4.6); glutamate dehydrogenase (EC 1.4.1.3). metabolism pathways in the rat placenta at different stages of foetal development; and thus, the activities of alanine, aspartate and tyrosine transaminases, serine dehydratase, arginase, glutaniine synthetase, glutaminase, glutamate dehydrogenase and adenylate deaminase have been determined to ascertain the relative potential importance of placental amino nitrogen (and ammonia) pathways (Fig. 1) during the intra-uterine development with respect to the overall metabolic capabilities of the foetus. MATERIALS AND METHODS Female virgin albino Wistar rats, weighing ini- tially 156 zyxw k 4 g were used. The animals were left with adult males in individual cages until impregnation (observed by presence of spermatozoa in daily vaginal smears), when they were transferred to individual solid-bottomed cages with bedding and nesting material. All animals were housed in an environment with controlled light (12 h on/12 h zyx off) and tem- perature (22 rt_ 1 "C). They had free access to rat chow pellets and water. The rats were sacrificed with a guillotine at the beginning of a light cycle at 12, 19 or 21 days after impregnation. The foetuses and placentae, obtained by