Hepatic purine enzymes and uric acid excretion as indicators of protein quality in chicks fed graded L‐lysine diets

Abstract

AbstractIndicators of protein metabolism may be used in protein quality determination since they respond very rapidly to the quantity and quality of the protein consumed. Accordingly, in this study, the uric acid excretion and the hepatic activity of the purine enzymes nucleoside phosphorylase (EC 2.4.2.1) and xanthine dehydrogenase (EC 1.2.3.7) measured in chickens were correlated with the results obtained with two traditional methods used in protein quality evaluation such as protein efficiency ratio (PER) and net protein ratio (NPR). Data were obtained using diets prepared with single amino acid mixtures which provided 0, 5, 10, 25, 50 and 100% of the chicken lysine requirements. These mixtures provided a gradual increase in protein quality and were also tested in rats. The high correlation coefficients obtained when the results of PER or NPR were compared with the uric acid excretion or with the activities of both enzymes, suggest a practical use of these indicators in protein quality evaluation. This possibility was supported by the fact that the PER and NPR values of the mixtures measured in the chickens were similar to those obtained with rats with correlation coefficients between both species higher than 0.9.