Combination of Derivatization–HPLC–MS and Enzymatic Hydrolysis–Edman Degradation for Amino Acid Sequence and Configuration of Polymyxin B Components

An analysis strategy that can simultaneously determine the amino acid site information and configuration for polymyxin (PM) components is reported in this study. The main components of PMB1, PMB2, and PMB1-I (the Leucine at position 7 changed to be Isoleucine) were purified from the mixture of PMB. The PMB component was hydrolyzed by hydrochloric acid to be a mixture of amino acids, which were derivatized with Marfey’s reagent of N α -(5-fluoro-2,4-dinitrophenyl)- l -alanine amide ( l -FDAA), and then, the configurations of amino acids were easily determined by HPLC–MS. However, the aforementioned method could not offer the information of amino acid at each site, a specific enzymatic hydrolysis method combined Edman degradation was developed. The fatty acyl-diaminobutyric acid (position 1) of PMB component was removed by ficin, and the PMB components were transformed to be PMB nonapeptide. The amino acids at each site of the nonapeptide were determined by N-terminal sequencing. Combining the results of the above methods, the amino acid information and configuration of each site in PM components can be determined, especially the l -Leucine and l -Isoleucine in PMB1 and PMB1-I. The workflow was useful for other PM analogues to identify the sequence and configuration for quality control.