Sulfur-36S stable isotope labeling of amino acids for quantification (SULAQ).

We introduce a universal metabolic labeling strategy using elemental heavy 36Sulfur (36S) called 36Sulfur stable isotope labeling of amino acids for quantification (SULAQ). In the proof of principle experiment, Pseudomonas putida KT2440 was grown in defined minimal medium with sodium benzoate or sodium succinate as the sole carbon and 32S- or 36S-sodium sulfate as the sole sulfur sources. Quantification using mass spectrometry resulted in 562 proteins with 1991 unique peptides. SULAQ technology can be a valuable alternative strategy for the quantitative comparisons in MS-based proteomics approaches characterizing bacterial and other biological samples in different growth conditions.