Protein/peptide hormones

Describe biochemical and functional distinctions among steroid hormones, protein/peptide hormones, and amine hormones... 

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

Protein/peptide hormones are derived from amino acids. These hormones are preformed and stored for future use in membrane-bound secretory granules. When needed, they are released by exocytosis. Protein/peptide hormones are water soluble, circulate in the blood predominantly in an unbound form, and thus tend to have short half-lives. Because these hormones are unable to cross the cell membranes of their target tissues, they bind to receptors... 

Table 10.1 Distinguishing Features of Steroid, Protein/Peptide, and Amine Hormones... 

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.

Steroid hormones and thyroid hormone carry out their effects by way of gene activation. In contrast to the protein/peptide hormones, which alter existing enzyme activity, these hormones induce the synthesis of new enzymes that then influence cellular metabolism. 

Protein, peptide, and/or carbohydrate products produced by cell culture (other than antibiotics and hormones)... 

Pituitary ACTH Antidiuretic hormone (ADH) Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) Growth hormone (GH) Oxytocin Prolactin Thyroid-stimulating hormone (TSH) Peptides or proteins... 

The parathyroid hormone receptor 1 (PTHRl) protein belongs to the GPCR family B. The PTHRl is a receptor for PTH and for parathyroid hormone-related peptide... 

Chantalat, L., Jones, N. D., Korber, F. et al. (1995). The crystal structure of wild-type growth hormone at 2.5A resolution. Protein Peptide Lett. 2, 333. 

Further, fish protein hydrolysates contain hormone-like peptides and growth factors that accelerate calcium absorption (Fouchereau-Peron et ah, 1999). These peptides are capable of binding to the cell surface receptors on osteoclasts and have a role in calcium metabolism by decreasing the number of osteoclasts. Therefore, these peptides could be used in the treatment of osteoporosis and Paget s disease. Further,... 

Reports of biosensors for proteins/peptides other than hormones and immunoglobulins... 

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