Characterization of succinimide‐type dehydration products of recombinant hirudin variant 1 by electrospray tandem mass spectrometry

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Abstract
Two congeners Q4 and Q5 inferred in earlier analyses to be cyclic succinimide‐type dehydration product; of recombinant hirudin (variant 1) were structurally fully characterized. After isotopic labeling by ring‐opening with H218O, the suspected anhydro‐positions Asp53 and Asp33 were confirmed by tandem mass spectrometry (MS/MS) sequencing of relevant smaller peplides directly in the enzymatic hydrolysates (V8 protease) using electrospray MS/MS. The chosen strategy proved highly efficient and sensitive.