Catecholamines protein/peptide hormones

Feature Steroid hormones Protein/peptide hormones Amine hormones Thyroid hormones Catecholamines ... 

The catecholamines are biologically similar to protein/peptide hormones. These hormones are soluble in the blood and are transported in an unbound form. Therefore, the catecholamines have a relatively short half-life. Because these hormones do not cross cell membranes, they bind to receptors on the membrane surface. Finally, the catecholamines are stored intracellu-larly in secretory granules for future use. 

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

Figure 10.1 ThecyclicAMPsecondmessengersystem.Themostcommonsecond messenger system activated by the protein/peptide hormones and the catecholamines involves the formation of cAMP. This multistep process is initiated by binding of the hormone (the first messenger) to its receptor on the cell surface. The subsequent increase in the formation of cAMP (the second messenger) leads to the alteration of enzyme activity within the cell. A change in the activity of these enzymes alters cellular metabolism.

Electrophoresis on a macro scale has been applied to a variety of difficult analytical separation problems inorganic anions and cations, amino acids, catecholamines, drugs, vitamins, carbohydrates, peptides, proteins, nucleic acids, nucleotides, polynucleotides, and numerous other species. A particular strength of electrophoi esis is its unique ability to separate charged macromolecules of interest to biochemists, biologists, and clinical chemists. For many years, electrophoresis has been the powerhouse method of separating proteins (enzymes, hormones, antibodies) and nucleic acids (DNA, RNA), for which it offers unparalleled resolution. ... 

The major cell types of the adrenal medulla and extra-adrenal paraganglia include the catecholamine-synthesizing cells and the supporting or sustentacular cells. ° Both catecholamines and catecholamine-synthesizing enzymes have been demonstrated in the former cells with immunofluorescent techniques in frozen sections and immunoperoxidase techniques in paraffin-embedded material.The catecholamine-synthesizing cells typically exhibit positivity for a variety of generic NE markers and are variably positive for certain peptide hormones. Sustentacular cells, in contrast, are positive for S-100 protein. ... 

Animal hormones essentially fall into four different chemical classes (1) amine-derived hormones, (2) peptide/protein hormones, (3) steroid hormones, and (4) lipid or phospholipid hormones. Amine-derived hormones such as catecholamines and thyroxine are derivatives of the amino acids tyrosine and tryptophan. Peptide hormones including insulin, growth hormone, and vasopressin consist of polypeptides ranging in length from 5 to 200 residues. Steroid hormones such as estrogen... 

Thyroxine and catecholamine are examples of hormones that are derived from amino acids they are water soluble and circulate in plasma either bound to proteins (thyroxine) or free (catecholamines). Thyroxine binds avidly to three binding proteins and has a half-life of about 7 to 10 days, and the free and unbound catecholamines such as epinephrine have a very short half-life of a minute or less. As do the water-soluble peptide and protein hormones, these hormones interact with membrane-associated receptors and use a second messenger system. 

Cell surface receptors, which detect water-soluble hormones that do not enter the cell (peptides, proteins, glycoproteins, catecholamines). The mechanism of action of each of these receptor types is different because each is associated with different postreceptor events in the cell. 

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