Nutritional Evaluation of Glycated Valine and Tryptophan as a Precursor for Protein Synthesis in Chicken Embryo Myoblasts

Abstract

Valine and Tryptophan play a role of being a precursor for protein synthesis. Glycation is a non-enzymatic reaction causing dehydrating condensation between the carbonyl group of glucose and the α-amino group of amino acids. Glycation of tryptophan forms two types of glycated compounds, Amadori product and (1R,3S)-1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (PHP-THβC). In case of valine, only Amadori product is formed by glycation. These compounds are lack of the α-amino group, which might not make glycated amino acids be a precursor for protein synthesis. It is known that glycation proceeds more readily in chickens than in mammals because hyperglycemia and high body temperature are features in avian species. In this study, therefore, we attempted to evaluate nutritional value of glycated valine and tryptophan as a precursor for protein synthesis. Myoblasts from chicken embryos were incubated in valine or tryptophan-free medium supplemented with or without insulin-like growth factor-I (IGF-I). In this cell culture system, the effect of glucose-valine Amadori product supplemented in the valine deficient medium was compared to that of supplemented valine. The effect of PHP-THβC supplementation was also examined. Protein synthesis and degradation of myoblasts were measured using a radioactive tracer, [3H]-phenylalanine. Protein synthesis of chicken embryo myoblasts was not affected by the addition of glucose-valine Amadori product into valine-deficient medium. When IGF-I was added in the medium, and the addition of PHP-THβC into tryptophan-deficient medium increased protein synthesis of chicken embryo myoblasts, but the extent of elevation of protein synthesis was lower than that in case of tryptophan supplementation into tryptophan-deficient medium. In the absence of IGF-I, PHP-THβC did not increase protein synthesis. These results suggest that valine-glucose Amadori product and PHP-THβC does not have nutritional value for being a precursor of protein synthesis.

Keywords

• glycation
• myoblast
• protein degradation
• protein synthesis
• tryptophan
• valine