Hormone Classification: Tryptophan Derivatives

Hormone Classification

• Hormones are classified by their proximity to the site of action (autocrine, paracrine, endocrine, neuroendocrine, pheromones) and chemical structure (proteins/peptides, steroids, amino acid derivatives, eicosinoids).
• Solubility in aqueous media is another important classification; hormones can be hydrophobic or hydrophilic.

Hormone Classification: Chemical Structure: AA Derivatives

• Hormones are derived from tyrosine and tryptophan.
• Examples of hormones derived from tryptophan include: L-tryptophan, 5-Hydroxytryptophan, Serotonin, N-acetylserotonin, and Melatonin.

Hormone Derivatives of Tryptophan

• L-Tryptophan is the precursor to 5-hydroxytryptophan.
• 5-hydroxytryptophan is converted to serotonin by the enzyme 5-hydroxytryptophan decarboxylase.
• Serotonin is converted to N-acetylserotonin by the enzyme serotonin N-acetyltransferase (NAT).
• N-acetylserotonin is converted to melatonin by the enzyme hydroxyindole-O-methyltransferase.

Functions of Melatonin

• Melatonin possesses anti-inflammatory, anti-oxidative, immunomodulatory, cardioprotective, and neuroprotective functions.
• It also plays a role in melanogenesis, metabolism regulation, and fixing sleep dysfunction.
• It also acts as a circadian rhythms modulator.

Hormone Derivatives of Tyrosine

• Tyrosine is a precursor to other hormones.
• Examples include: DOPA, Dopamine, Noradrenaline, and Adrenaline.
• These hormones are derived from each other via enzyme mediated conversions.

Protein or Peptide Hormones

• Protein or peptide hormones can be shorter chain peptides, larger proteins, or glycoproteins.
• Examples include Oxytocin and Growth hormone.

Peptide Hormones

• Oxytocin is a peptide hormone.
• Its structure is a chain of amino acids (Gly, Leu, Pro, Cys, Asp, Glu, Cys, Tyr, Ile).

Protein Hormone

• Growth hormone is a protein hormone
• Its structure is depicted schematically as a circular pattern with different amino acids (e.g. Arg, Tyr, Leu, Asn, Ser, etc)

Glycoprotein Hormones

• Glycoprotein hormones are a family of protein hormones.
• They include alpha and beta subunits.
• The alpha subunit is common
• Specificity resides in the beta subunit.
• Examples include TSH, LH, EPO, hCG, Inhibin.

Lipid Derived Hormones

• Lipid derived hormones are derived from Cholesterol.
• They include steroids like Androgens (Testosterone), Oestrogens (Estradiol), and Progestins (Progesterone).
• The adrenocortical group includes glucocorticoids (Cortisol) and mineralocorticoids (Aldosterone).

Lipid Derived Hormones: Eicosanoids

• Eicosanoids derive from omega-3 or omega-6 fatty acids.
• They include prostaglandins (PGs), thromboxanes, and leukotrienes.

Chemical Structure Determines

• Chemical structure directly influences hormone synthesis, storage, release, transport in body fluids, receptor location, mechanism of action, and degradation.

Hormone Synthesis and Storage : Protein/Peptide Hormones

• Synthesis of protein/peptide hormones takes time.
• Hormones are stored in vesicles.
• These vesicles act as reservoirs for the hormones.

Basic Steps in Making a Protein/Peptide Hormone

• The basic steps involve gene transcription to primary RNA transcript to messenger RNA, to translation, prepeptide/prepropeptide, and post-translational modification for mature (active) peptide hormone, finally secretion.

Synthesis of peptide hormones : steps

• Hormones are synthesized in ribosomes on the rough endoplasmic reticulum (ER), then transported to the Golgi apparatus, where they are processed and packaged into secretory vesicles.
• Hormones are then stored in secretory vesicles within the cell until they are released.

Hormone Synthesis and Storage: Steroid Hormones

• Steroid hormones are derived from cholesterol
• Formed in mitochondria and smooth endoplasmic reticulum.
• Synthesized and released immediately.
• Lipid soluble, thus permeable to membranes.
• Not stored in cells

Steroid Hormones Pathway

• Cholesterol is the precursor for the majority of steroid hormones.
• The transformation follows enzymatic pathways.
• Examples include pathways to testosterone and estradiol, and glucocorticoids and mineralocorticoids.

Steroid transformation in target cells

• Steroid hormones bind to receptors.
• The transformed hormone enters the cytoplasm and subsequently the nucleus.
• The steroid activates specific gene expressions.

Protein/peptide vs steroid-mediated secretion

• Proteins/peptides are synthesized and stored in secretory vesicles, relying on exocytosis for release.
• Steroids are immediately released from the steroid-secreting cells.

Insulin Synthesis

• Insulin is a protein/peptide hormone synthesized in steps from preproinsulin, proinsulin to mature insulin.

Multiple Processing Patterns for Protein Hormones

• Preprohormones are processed into active hormones and other peptides.
• Different hormones may be produced from a single preprohormone structure, as demonstrated by ACTH, glipotropins, beta-endorphin fragments.

Hyperpigmentation

• Images of hyperpigmentation (unusual darkening) are shown.

Explore the classification of hormones, focusing on the derivatives of tryptophan. This quiz will test your knowledge of hormone types, their chemical structures, and the processes involved in the synthesis of key hormones like serotonin and melatonin.