Hormone Classification and Derivatives

Hormone Classification

• Hormones are classified by their proximity to the site of action (autocrine, paracrine, endocrine, neuroendocrine, pheromones) and by their chemical structure (proteins/peptides, steroids, amino acid derivatives, eicosanoids).
• Solubility in aqueous media dictates how hormones are transported (hydrophobic or hydrophilic).

Hormone Derivatives of Tyrosine and Tryptophan

• Hormones are derived from amino acids tyrosine and tryptophan, and exist in various forms.
• L-tryptophan is a precursor and leads to the production of 5-hydroxytryptophan.
• 5-hydroxytryptophan is converted to serotonin.
• Serotonin is then converted by N-acetyltransferase (NAT) to N-acetylserotonin which is later converted to melatonin.

Hormone Derivatives of Tyrosine

• Tyrosine is a precursor to several important hormones like dopamine, noradrenaline, and adrenaline.
• These hormones are derived from tyrosine via enzymatic reactions (Aromatic Amino Acid Decarboxylase (AAD) and Dopamine beta-hydroxylase (DBH) and Phenylethanolamine-N-methyltransferase (PNMT)).

Peptide/Protein Hormones

• Peptide hormones include shorter chain peptides, larger proteins, and glycoproteins.
• Oxytocin is a peptide hormone.
• Growth hormone is a protein hormone.
• Examples of glycoprotein hormones are TSH, LH, EPO, hCG, and Inhibin.

Lipid Derived Hormones

• Cholesterol is the precursor of steroid hormones, which are a class of lipid-derived hormones.
• Gonadal steroid hormones include androgens (testosterone), estrogens (estradiol), and progestins (progesterone).
• Adrenocortical steroid hormones include glucocorticoids (cortisol), mineralocorticoids (aldosterone).
• Eicosanoids are lipid mediators derived from arachidonic acid, including prostaglandins (PGs), thromboxanes, and leukotrienes.

Chemical Structure Determines

• A hormone's chemical structure dictates its synthesis, storage, release, transport within the body, receptor location, mechanism of action, and degradation.

Hormone Synthesis and Storage

• Protein/peptide hormones are synthesized through a multi-step process involving transcription, translation, and post-translational modifications.
• These hormones are stored in vesicles until needed.
• Release occurs through exocytosis
• The bi-lipid membrane doesn't allow these hormones to pass through so they need exocytosis.

Synthesis of Insulin

• Insulin is a protein hormone created through several steps, starting with preproinsulin which becomes proinsulin and then finally to insulin.

Multiple Processing Patterns for Protein Hormones

• Preprohormones undergo processing to form the final active hormone and other fragments.
• Pro-opiomelanocortin (POMC) is an example of a prohormone that produces various hormones/fragments

Steroid Hormones

• Steroid hormones are derived from cholesterol.
• Enzymes in mitochondria and smooth endoplasmic reticulum (ER) are essential in the synthesis process.
• Steroid hormones are immediately released and are not packaged.
• These hormones are highly lipid-soluble and readily cross cell membranes.

Major Pathways in Steroid Biosynthesis

• Specific enzymes (like CYP17, 3β-HSD, CYP21A2, CYP11B1, CYP11B2) catalyze various steps in the conversion of cholesterol to different steroid hormones.
• Pathways lead to steroid hormones like cortisol, aldosterone, estrogens, and androgens.

Steroids can be transformed to active steroid in target cell

• Steroids can go through transformations in the target cell in order to become an active steroid hormone.

Protein/Peptide vs Steroid Secreting Cells

• Protein/peptide secreting cells have a different structure than steroid secreting cells.

Explore the classification of hormones based on their proximity to action and their chemical structure. Learn about the derivatives of tyrosine and tryptophan, including the conversion processes leading to vital hormones like serotonin and melatonin.