Long-term ingestion of ammonium increases acetylglutamate and urea levels without affecting the amount of carbamoyl-phosphate synthase

Authors


Correspondence to S. Grisolía, Instituto de Investigaciones Citologicas de la Caja de Ahorros de Valencia, Amadeo de Saboya, E-46010 Valencia, Spain

Abstract

Rats were fed the following diets: standard (20% protein), high-protein (80%), protein-free, standard plus ammonium and protein-free plus ammonium for six weeks. The standard plus ammonium diet was prepared to contain ammonia equivalent to that supplied by the high-protein diet. Addition of ammonium acetate 20% by mass) to the 20% protein or protein-free diets results in 2.3- and 10-fold increases of urea excretion respectively, without increase of carbamoyl-phosphate synthase.

Supplementation of the standard diet with ammonium increases the mitochondrial content of acetylglutamate from 830 to 1590 pmol/mg protein, and of the protein-free diet from 130 to 1040 pmol/mg. However, ingestion of ammonium did not increase the activity of acetylglutamate synthase. Therefore the efflux of acetylglutamate from mitochondria was determined. After 30 min at 37°C liver mitochondria from rats on standard diet released 61% of the initial acetylglutamate while mitochondria from animals on standard plus ammonium diet released only 20%. These results indicate that ingestion of ammonium increases the content of acetylglutamate in rat liver by decreasing its efflux from mitochondria. This effect is similar to that produced in mice by a high protein diet [Morita et al. (1982) J. Biochem. (Tokyo) 91, 563-569]. However while the high-protein diet increases carbamoyl-phosphate synthase content, the ammonium diet does not.

Abbreviation
CPS

carbamoyl-phosphate synthase

Enzymes
 

Carbamoyl-phosphate synthase (ammonia) (EC 6.3.4.16)

acetylglutamate synthase

amino-acid transacetylase (EC 2.3.1.1)

Ancillary