Probing Methionine Uptake in Live Cells by Deuterium Labeling and Stimulated Raman Scattering

The small biomolecule methionine (Met) is a fundamental amino acid required for a vast range of biological processes such as protein synthesis, cancer metabolism, and epigenetics. However, it is still difficult to visualize the subcellular distribution of small biomolecules including Met in a minimally invasive manner. Here, we demonstrate stimulated Raman scattering (SRS) imaging of cellular uptake of deuterated methionine (d(8)-Met) in live HeLa cells by way of comparison to the previously used alkyne-labeled Met analogue-homopropargylglycine (Hpg). We show that the solutions of d(8)-Met and Hpg have similar SRS signal intensities. Furthermore, by careful image analysis with background subtraction, we succeed in the SRS imaging of cellular uptake of d(8)-Met with a much greater signal intensity than Hpg, possibly reflecting the increased and minimally invasive uptake kinetics of d(8)-Met compared with Hpg. We anticipate that d(8)-Met and other deuterated biomolecules will be useful for investigating metabolic processes with subcellular resolution.