A method for efficient isotopic labeling of recombinant proteins

A rapid and efficient approach for preparing isotopically labeled recombina nt proteins is presented. The method is demonstrated for C-13 labeling of t he C-terminal domain of angiopoietin-2, N-15 labeling of ubiquitin and for H-2/C-13/N-15 labeling of the Escherichia coli outer-membrane lipoprotein L pp-56. The production method generates cell mass using unlabeled rich media followed by exchange into a small volume of labeled media at high cell den sity. Following a short period for growth recovery and unlabeled metabolite clearance, the cells are induced. The expression yields obtained provide a fourfold to eightfold reduction in isotope costs using simple shake flask growths.