Lactose takes years to break down on its own. But if exposed to the protein lactase, the reaction proceeds very quickly, while lactase itself remains unchanged. Lactase is an example of a(n) .

Enzyme  

Explanation:

An enzyme is an organic catalyst that speeds up a reaction but can be recovered unchanged.

Human lactase consists of 4092 amino acid groups and has a molar mass of about 280 000 u, so it has a complex structure.

2b2t

explanation:

2b2t

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