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In the case of normal RNase A, Anfisen found that oxidizing the Cys residues before slowly removing the urea gave a very different result than oxidizing the Cys after slowly removing the urea. When the urea was removed first, Anfisen recovered 100% of the catalytic activity. When the urea was removed after oxidation, only about 1% of the activity (1/105) was recovered. The conclusion was that 104 of every 105 molecules was misfolded, and therefore catalytically inactive. Let's say someone raises an objection to this interpretation, and says that perhaps, instead, something chemically happens to the active site of RNase A when it is oxidized before refolding, and that the ~1% activity measured represents the residual and greatly reduced enzyme activity of all of the molecules, and the number is just coincidently similar to 1/105. (In other words, instead of 104 completely inactive molecules for every 1 completely active molecule, all molecules are equally damaged, and only function at 1% activity due to some change in all of their enzyme active sites). A good scientist can't simply dismiss this alternative explanation as improbable, but instead could design another compelling control experiment to test (and potentially rule out) this alternative hypothesis. What simple and straightforward experiment, urea and a reducing agent as Anfisen did, could be performed, using either wild-type RNase A, or a mutation, to test the objection?

In the case of normal RNase A, Anfisen found that oxidizing the Cys residues before slowly removing the urea gave a very different result than oxidizing the Cys after slowly removing the urea. When the urea was removed first, Anfisen recovered 100% of the catalytic activity. When the urea was removed after oxidation, only about 1% of the activity (1/105) was recovered. The conclusion was that 104 of every 105 molecules was misfolded, and therefore catalytically inactive. Let's say someone raises an objection to this interpretation, and says that perhaps, instead, something chemically happens to the active site of RNase A when it is oxidized before refolding, and that the ~1% activity measured represents the residual and greatly reduced enzyme activity of all of the molecules, and the number is just coincidently similar to 1/105. (In other words, instead of 104 completely inactive molecules for every 1 completely active molecule, all molecules are equally damaged, and only function at 1% activity due to some change in all of their enzyme active sites). A good scientist can't simply dismiss this alternative explanation as improbable, but instead could design another compelling control experiment to test (and potentially rule out) this alternative hypothesis. What simple and straightforward experiment, urea and a reducing agent as Anfisen did, could be performed, using either wild-type RNase A, or a mutation, to test the objection?

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
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In the case of normal RNase A, Anfisen found that oxidizing the Cys residues before slowly removing the urea gave a very different result than oxidizing the Cys after slowly removing the urea. When the urea was removed first, Anfisen recovered 100% of the catalytic activity. When the urea was removed after oxidation, only about 1% of the activity (1/105) was recovered. The conclusion was that 104 of every 105 molecules was misfolded, and therefore catalytically inactive. Let's say someone raises an objection to this interpretation, and says that perhaps, instead, something chemically happens to the active site of RNase A when it is oxidized before refolding, and that the ~1% activity measured represents the residual and greatly reduced enzyme activity of all of the molecules, and the number is just coincidently similar to 1/105. (In other words, instead of 104 completely inactive molecules for every 1 completely active molecule, all molecules are equally damaged, and only function at 1% activity due to some change in all of their enzyme active sites). A good scientist can't simply dismiss this alternative explanation as improbable, but instead could design another compelling control experiment to test (and potentially rule out) this alternative hypothesis. What simple and straightforward experiment, urea and a reducing agent as Anfisen did, could be performed, using either wild-type RNase A, or a mutation, to test the objection?
Transcribed Image Text:In the case of normal RNase A, Anfisen found that oxidizing the Cys residues before slowly removing the urea gave a very different result than oxidizing the Cys after slowly removing the urea. When the urea was removed first, Anfisen recovered 100% of the catalytic activity. When the urea was removed after oxidation, only about 1% of the activity (1/105) was recovered. The conclusion was that 104 of every 105 molecules was misfolded, and therefore catalytically inactive. Let's say someone raises an objection to this interpretation, and says that perhaps, instead, something chemically happens to the active site of RNase A when it is oxidized before refolding, and that the ~1% activity measured represents the residual and greatly reduced enzyme activity of all of the molecules, and the number is just coincidently similar to 1/105. (In other words, instead of 104 completely inactive molecules for every 1 completely active molecule, all molecules are equally damaged, and only function at 1% activity due to some change in all of their enzyme active sites). A good scientist can't simply dismiss this alternative explanation as improbable, but instead could design another compelling control experiment to test (and potentially rule out) this alternative hypothesis. What simple and straightforward experiment, urea and a reducing agent as Anfisen did, could be performed, using either wild-type RNase A, or a mutation, to test the objection?
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