Final answer:
The two classes of amino acid-derived hormones are catecholamines and thyroid hormones, differentiated by their iodine content. Catecholamines include hormones like epinephrine and norepinephrine, while thyroid hormones include thyroxine and triiodothyronine.
Step-by-step explanation:
The two classes of amino acid-derived hormones are catecholamines and thyroid hormones. The characteristic that differentiates these two classes is their iodine content. Catecholamines, which include epinephrine and norepinephrine, are synthesized from the amino acid tyrosine and are secreted by the adrenal medulla. On the other hand, thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), are produced by the thyroid gland and their unique structure includes the incorporation of iodine atoms.