Enzymatic Synthesis and Characterization of l-Methionine and 2-Hydroxy-4-(methylthio)butanoic Acid (HMB) Co-oligomers

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Abstract
Oligomers of l-methionine (Met) and its hydroxy analogue, 2-hydroxy-4-(methylthio)butanoic acid (d,l-HMB) were synthesized with the proteolytic enzyme papain. The Met homooligomers and HMB−Met co-oligomers obtained through the enzymatic reactions were subjected to persulfonation and separated with reverse phase liquid chromatography (RPLC). The separated oligomers were characterized with electrospray ionization-mass spectrometry (ESI-MS). The oligomers were also characterized with matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS). The results showed that co-oligomers were predominantly composed of 4−8 Met residues and one HMB residue. The data also suggest that in the co-oligomers, HMB is attached at the N-terminal end of the oligopeptide chain. Keywords: Oligopeptides; co-oligomers; methionine; methionine hydroxy analogue; MHA; HMB; papain; mass spectrometry