MCAT AAMC BB Section Bank #27

[Wow-Zero]

Which statement regarding STRA6-mediated retinol uptake is best supported by the passage?

1. Retinol uptake activity by STRA6 is limited without the presence of intracellular binding proteins.
2. The expression of STRA6 is likely to be higher in the liver than in target organs.
3. Retinol uptake activity by STRA6 is accelerated when retinol is stored as intracellular retinol rather than as retinyl esters.
4. Binding of holo-RBP to STRA6 is likely to have a Hill coefficient greater than 1.

Does anyone know why 4 is wrong?

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[JimKimSlim]

I don’t have access to the passage you’re referring to, but a hill coefficient greater than 1 means the enzyme displays cooperativity (sigmoidal binding curve). Did the passage indicate any cooperativity in the enzyme?