Epinephrine, insulin, and auxins are all examples of that help produce feedback.
cofactors
enzymes
chemical transmitters

cofactors.

Explanation:

Epinephrine, insulin and auxins are cofactors.

Cofactors are non protein substance which activate enzymes activity by increasing the rate of chemical reaction of enzymes. They are organic molecules and they assist in enzyme activity. They exist in performing some reactions the enzymes cannot perform alone.

For example, insulin activate enzyme hexokinase which phosphorylate glucose.

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