Discussion
Identify the constituents of metalloenzymes:
1. Copper
2. Nickel
3. Zinc
4. Iron
Choose the most appropriate answer from the options given below:
Answer: D
The keyed answer is 1, 3 and 4: copper, zinc and iron.
A metalloenzyme has a metal ion bound in its structure that it needs to work. The classical human examples are zinc (carbonic anhydrase, alcohol dehydrogenase), copper (cytochrome c oxidase, superoxide dismutase, tyrosinase) and iron (catalase, the cytochromes). These three trace elements are the ones nutrition texts name together.
Nickel (2) is found in a few enzymes such as urease in plants and bacteria, but it is not counted among the metals of human metalloenzymes in the usual lists, which is why the options containing it are wrong. Option A leaves out iron, and no option offers all four metals, so 1, 3 and 4 is the best fit.
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