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Peptide hormones and protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocrine system of animals, including humans.〔(''Peptide Hormone Secretion/Peptide Hormone Action: A Practical Approach,'' ) K. Siddle, J. C. Hutton, Oxford University Press, 1991, ISBN 0-19-963073-9.〕 Most hormones can be classified as either amino acid–based hormones (amine, peptide, or protein) or steroid hormones. The former are water-soluble and act on the surface of target cells via second messengers; the latter, being lipid-soluble, move through the plasma membranes of target cells (both cytoplasmic and nuclear) to act within their nuclei. Like all peptides and proteins, peptide hormones and protein hormones are synthesized in cells from amino acids according to mRNA transcripts, which are synthesized from DNA templates inside the cell nucleus. Preprohormones, peptide hormone precursors, are then processed in several stages, typically in the endoplasmic reticulum, including removal of the N-terminal signal sequence and sometimes glycosylation, resulting in prohormones. The prohormones are then packaged into membrane-bound secretory vesicles, which can be secreted from the cell by exocytosis in response to specific stimuli (e.g. --an increase in Ca2+ and cAMP concentration in cytoplasm).〔(''Peptide Hormone Secretion: A Practical Approach,'' ) J. C. Hutton, Hull University Press, 1991, ISBN 0-19-963068-2.〕 These prohormones often contain superfluous amino acid residues that were needed to direct folding of the hormone molecule into its active configuration but have no function once the hormone folds. Specific endopeptidases in the cell cleave the prohormone just before it is released into the bloodstream, generating the mature hormone form of the molecule. Mature peptide hormones then travel through the blood to all of the cells of the body, where they interact with specific receptors on the surfaces of their target cells. Some neurotransmitters are secreted and released in a similar fashion to peptide hormones, and some 'neuropeptides' may be used as neurotransmitters in the nervous system in addition to acting as hormones when released into the blood. When a peptide hormone binds to a receptor on the surface of the cell, a second messenger appears in the cytoplasm, which triggers signal transduction leading to the cellular responses.〔(''The Practice of Medicinal Chemistry,'' ) C. G. Wermuth, Academic Press, 2003, ISBN 0-12-744481-5.〕 Some peptide/protein hormones (angiotensin II, basic fibroblast growth factor-2, parathyroid hormone-related protein) also interact with intracellular receptors located in the cytoplasm or nucleus by an intracrine mechanism.〔(''The Endocrine System in Sports and Exercise,'' ) William J. Kraemer, Alan D. Rogol, Blackwell Publishing, 2005, ISBN 1-4051-3017-2.〕 ==Notable peptide hormones== Several important peptide hormones are secreted from the pituitary gland. The anterior pituitary secretes three: prolactin, which acts on the mammary gland; adrenocorticotropic hormone (ACTH), which acts on the adrenal cortex to regulate the secretion of glucocorticoids; and growth hormone, which acts on bone, muscle, and the liver. The posterior pituitary gland secretes antidiuretic hormone, also called vasopressin, and oxytocin. Peptide hormones are produced by many different organs and tissues, however, including the heart (atrial-natriuretic peptide (ANP) or atrial natriuretic factor (ANF)) and pancreas (glucagon, insulin and somatostatin), the gastrointestinal tract (cholecystokinin, gastrin), and adipose tissue stores (leptin).〔(''Dictionary of Biological Psychology,'' ) Philip Winn, Taylor and Francis, 2001, ISBN 0-415-13606-7.〕〔(''McGraw-Hill Encyclopedia of Science & Technology,'' ) Sybil P. Parker, McGraw-Hill, 1997, ISBN 0-07-911504-7.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Peptide hormone」の詳細全文を読む スポンサード リンク
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