The amino acid responsible for the Hopkins-Cole reaction is tryptophan.

Here's why:

* Hopkins-Cole Reaction: This reaction is a colorimetric test used to detect the presence of tryptophan in a protein sample.

* Mechanism: The reaction involves the interaction of tryptophan with a reagent called glyoxylic acid in the presence of concentrated sulfuric acid. This interaction results in the formation of a violet-colored complex, indicating the presence of tryptophan.

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