Sulfhydryl groups have die ability to react with die alkylating reagent N-ethylm

Question

Sulfhydryl groups have die ability to react with die alkylating reagent N-ethylmaleimide (NHM) in chemical modification experiments. When NHM is added to a purified solution of creatine kinase, Cys 278 is alkylated, but no other Cys residues in the protein are modified. What can you infer about the Cys 278 residue based on this observation? Based on the result described in Question 1, the investigators used the technique of site-directed mutagenesis to synthesize five mutant creatine kinase proteins in which the Cys 278 was replaced with either a Gly, Ser, Ala, Asn or Asp residue.

Explanation / Answer

1. From the observation, NEM is an alkylating agent and alkylate only Cys278 but not the other residues. Also, Cys278 may be having free -SH (thiol groups) as alkylating sites.

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