In the 1950s, Christian Anfinsen demonstrated the renaturation of the protein ri

Question

In the 1950s, Christian Anfinsen demonstrated the renaturation of the protein ribonuclease (RNase) in vitro. After reduction (to reduce the disulfide links) and the addition of urea (to denature the protein), the protein was in an unfolded state. After removing the urea and the reducing agent, the protein refolded, with greater than 90% activity. If the urea were removed after oxidation occurred, the protein had less than 5% activity. Why would the protein not refold correctly if the urea were removed after the reducing agent was removed? (In other words, what would happen if the urea were removed after oxidation?) Choose the best answer. O Disulfide bonds are not positioned correctly unless weak bonding interactions are present. O Urea would participate in weak bonding interactions with RNase, preventing oxidation of Cys. o Contaminants in the RNase preparation would form covalent bonds with the protein, O The protein would not fully unfold (denature). preventing reactivation.

Explanation / Answer

The protein not refold correctly if the urea were removed after the reducing agent was removed. This is because, disulfide bonds are not positioned correctly unless weak bonding interactions are present. If the urea is removed after reducing agent was removed, the cysteine residues in the enzyme may not form proper disulfide bridges in the correct orentation, which results in non-functional enzyme.

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