The use of electrospray mass spectrometry as a tool in analytical biochemistry was illustrated by determination of the molecular weights of wildtype and recombinant isopenicillin N synthase (IPNS). The molecular weight of recombinant IPNS produced using an expression system which generated soluble protein was found to be between 38 364 and 38 376 Da, ca 60 mass units higher than that of the wildtype material, consistent with the presence of an additional N-terminal glycine in the former. Observed molecular weights were all ca 70 Da higher than that calculated from sequence information, consistent with the complexion of a partially hydrated iron atom to the enzyme during analysis.
