<P> Water - soluble hormones include glycoproteins, catecholamines, and peptide hormones composed of polypeptides, e.g. thyroid - stimulating hormone, follicle - stimulating hormone, luteinizing hormone and insulin . These molecules are not lipid - soluble and therefore cannot diffuse through cell membranes . Consequently, receptors for peptide hormones are located on the plasma membrane because they have bound to a receptor protein located on the plasma membrane . </P> <P> Water - soluble hormones come from amino acids and are located and stored in endocrine cells until actually needed . </P> <P> The main two types of transmembrane receptor hormone receptor are the G - protein - coupled receptors and the enzyme - linked receptors . These receptors generally function via intracellular second messengers, including cyclic AMP (cAMP), cyclic GMP (cGMP), inositol 1, 4, 5 - trisphosphate (IP3) and the calcium (Ca) - calmodulin system . </P> <P> Steroid hormone receptors and related receptors are generally soluble proteins that function through gene activation . Lipid - soluble hormones target specific sequences of DNA by diffusing into the cell . When they have diffused into the cell, they bind to receptors (intracellular), and migrate into the nucleus . heir response elements are DNA sequences (promoters) that are bound by the complex of the steroid bound to its receptor . The receptors themselves are zinc - finger proteins . These receptors include those for glucocorticoids (glucocorticoid receptors), estrogens (estrogen receptors), androgens (androgen receptors), thyroid hormone (T3) (thyroid hormone receptors), calcitriol (the active form of vitamin D) (calcitriol receptors), and the retinoids (vitamin A) (retinoid receptors). Receptor - protein interactions induce the uptake and destruction of their respective hormones in order to regulate their concentration in the body . This is especially important for steroid hormones because many body systems are entirely steroid dependent . </P>

Where would the receptors for lipid-soluble hormones be found