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

beta -Alanine-oxoglutarate aminotransferase (beta -AlaAT I) and beta -alani ne-pyruvate aminotransferase (beta -AlaAT II) catalyze the transamination r eaction 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 pro tein 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 ha nd, the level of beta -AlaAT II activity in the kidney was slightly decreas ed by a protein-free diet. Neither beta -AlaAT I nor beta -AlaAT II activit ies in the kidney were affected by a high-protein diet. These results sugge sted that beta -alanine may be used efficiently in animals fed a protein-fr ee or low-protein diet because the kidney provides beta -alanine by means o f the hydrolysis of beta -alanyl-L-histidine (carnosine). The addition of b eta -alanine to the diet significantly activated beta -AlaAT I in the kidne ys 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 t he beta -alanine diet, and beta -AlaAT II activity was not detected.