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

Abstract

beta;-Alanine-oxoglutarate aminotransferase (β-AlaAT I) and β-alanine-pyruvate aminotransferase (β-AlaAT II) catalyze the transamination reaction of ω-amino acids such as β-alanine, β-aminoisobutyrate, and γ-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 β-AlaAT I and β-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 β-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 β-AlaAT II activity in the kidney was slightly decreased by a protein-free diet. Neither β-AlaAT I nor β-AlaAT II activities in the kidney were affected by a high-protein diet. These results suggested that β-alanine may be used efficiently in animals fed a protein-free or low-protein diet because the kidney provides β-alanine by means of the hydrolysis of β-alanyl-L-histidine (carnosine). The addition of β-alanine to the diet significantly activated β-AlaAT I in the kidneys of rats in accordance with changes in its mRNA level. In the rat brain, β-AlaAT I activity was not altered by the dietary protein level or by the β-alanine diet, and β-AlaAT II activity was not detected.