Protein hydrolysis and measurement

For protein hydrolysis and measurement, a previous protocol (Nanchen et al, 2007) was extended. The washed lysate was adjusted to 6 N by HCl addition. Acidified lysates were incubated for 1 h at 110°C and then dried under airflow at 65°C. Dried samples were silylated by dissolution in 50 μl dimethylformamide and then added to 100 μl L N‐tert‐butyldimethylsilyl‐N‐methyltrifluoroacetamide with 1% tertbutyldimethylchlorosilane. Reactions were then incubated at 85°C for 1 h. Products were measured on a 6890 GC combined with a 5973 Inert SL MS system (Agilent Technologies). Labeled fractions were adjusted for native isotope abundance (Nanchen et al, 2007).