[Judy]

Which statement is FALSE regarding flavoproteins?
A) They may contain either FMN or FAD.
B) The reduction potential of the flavin will depend on the amino acids in the polypeptide chain.
C) They will need at least two substrates in order to function as enzymes.
D) The are always integral membrane proteins.
E) Most flavoproteins in electron transport have a lower reduction potential than coenzyme Q.

Why B and C are correct?

For B, negatively charged amino acids in a protein could decrease the reduction potential of the flavin, and the other way round for positively charged ones, since negatively charged amino acids could 'share' or 'donate' some of their electrons to decrease the burden of extra reduction potential. Let me know if my thinking are right.

For C, I don't get why flavoprotein requires at least two substrate to function  as an enzyme?

[Babcock_Hall]

Inasmuch as both the oxidized and reduced forms are electrically neutral, I would not focus on the charge of the amino acids surrounding flavin.  I am not ready to buy into your model of sharing electron density.  However, the oxidized form is flat, and the reduced form is V-shaped.  Can you make a model starting with that idea?

One way to think about C is that flavin coenzymes are not released from the protein as part of the catalytic cycle.  Does that help?

[Judy]

Yes， Thanks for helping.