Two inhibitors are tested on an enzyme. With inhibitor X the rate at very high $[S]$ reaches the same plateau as without inhibitor, although a higher $[S]$ is needed. With inhibitor Y the plateau rate is lowered and raising $[S]$ does not restore it. The best conclusion is

AX is competitive and Y is non-competitive
BX is non-competitive and Y is competitive
Cboth X and Y are competitive
Dboth X and Y are non-competitive

Answer: A

A competitive inhibitor is outcompeted by excess substrate, so the maximum rate is regained. A non-competitive inhibitor binds elsewhere and lowers the number of active enzyme molecules, so the plateau cannot be restored by more substrate.

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Two inhibitors are tested on an enzyme. With inhibitor X the rate at very high [S] reaches the same plateau as without inhibitor, although a higher [S] is needed. With inhibitor Y the plateau rate is lowered and raising [S] does not restore it. The best conclusion is

Answer: A

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Two inhibitors are tested on an enzyme. With inhibitor X the rate at very high $[S]$ reaches the same plateau as without inhibitor, although a higher $[S]$ is needed. With inhibitor Y the plateau rate is lowered and raising $[S]$ does not restore it. The best conclusion is