Measurement of Protein Synthesis in an Imalt Issues in Vivo

Protein turnover, comprising the twin processes of protein synthesis and protein degradation, dictates protein balance. This chapter reviews the development of techniques for measurement of protein synthesis in animal tissues in vivo. It focuses on the conceptual, technical, and interpretive difficulties in commonly used approaches to measurement of protein synthesis in vivo and the manner with which these difficulties have been overcome. The amino acid pool used for protein synthesis may derive its amino acids from two sources — extracellular or from intracellular protein degradation. Measurements in gut mucosa of protein synthesis by the flooding dose method have indicated lower rates of protein synthesis compared to K_si determined during continuous infusion. To study protein turnover in larger animals, cost of isotope makes the flooding dose method expensive. Therefore, a continuous infusion procedure was developed which extended the time period available for labeled amino acid incorporation into protein, permitting use of less labeled precursor.