Protein synthesis in normal and inflamed states

Body protein is turned over by the continual and simultaneous processes of synthesis and degradation. Knowledge of the rates of protein synthesis and degradation may help define the mechanisms of physiological and pathophysiological metabolism. Dynamic biological processes such as these are most directly studied by the use of stable isotope-labeling methods. Following the administration of label, the amount of isotope contained in the precursor (aminoacyl-tRNA, AA-tRNA) and in the product (protein) is monitored over time and from these measurements the rate of synthesis can be derived. A long standing methodologic problem in the measurement of protein synthesis, however, has been how to accurately determine the amount of isotope contained in the precursor pool. Mass isotopomer distribution analysis (MIDA) is a technique based on combinatorial probability analysis and can be used to determine precursor enrichment and with it rates of synthesis of polymers such as protein. MIDA has been successfully used to measure the synthesis of small polymers (carbohydrates and lipids). Here the method was developed in vitro and in vivo for the measurement of protein biosynthesis.;The mass isotopomer pattern of peptides synthesized in vitro from labeled leucine was analyzed by electrospray ionization/mass spectrometry with either quadrupole or magnetic sector mass analyzers. Both instruments gave accurate and precise measurements of individual isotopomer abundances using appropriate curve-fitting strategies. MIDA was then used to measure the in vivo synthesis of rat serum albumin (RSA) in fed and fasted rats after administration of (...