Influence of dietary protein levels on beta-alanine aminotransferase expression and activity in rats

beta-Alanine-oxoglutarate aminotransferase (beta-AlaAT I) and beta-alanine-pyruvate aminotransferase (beta-AlaAT II) catalyze the transamination reaction of omega-amino acids such as beta-alanine, beta-aminoisobutyrate, and gamma-aminobutyrate, amino acids that are not protein constituents. The influence of dietary protein levels on the expression and activities of these enzymes was investigated by using male rats. Both beta-AlaAT I and beta-AlaAT II activities in the liver were increased with the level of protein in the diet in accordance with changes in their mRNA levels. However, the beta-AlaAT I activity in the kidney was increased by protein-free and low-protein diets in relation to changes in its mRNA level. On the other hand, the level of beta-AlaAT II activity in the kidney was slightly decreased by a protein-free diet. Neither beta-AlaAT I nor beta-AlaAT II activities in the kidney were affected by a high-protein diet. These results suggested that beta-alanine may be used efficiently in animals fed a proteinfree or low-protein diet because the kidney provides beta-alanine by means of the hydrolysis of beta-alanyl-L-histidine (carnosine). The addition of beta-alanine to the diet significantly activated beta-AlaAT I in the kidneys of rats in accordance with changes in its mRNA level. In the rat brain, beta-AlaAT I activity was not altered by the dietary protein level or by the beta-alanine diet, and beta-AlaAT II activity was not detected.