Схема. Два типа структуры предшественников полипептидных гормонов = Two configurations of precursors of polypeptide hormones.
Модификация: Melmed S., Polonsky K.S., Larsen P.R., Kronenberg H.M., Eds. Williams Textbook of Endocrinology, 12th ed., Saunders, 2011, 1816 p., см.: Физиология человека: Литература. Иллюстрации.
Примечание.
Two configurations of precursors of polypeptide hormones.
Diagrams represent the polypeptide backbones of protein sequences
encoded in messenger RNA (mRNA). One form of precursor consists of
the amino-terminal signal, or presequence, followed by the apoprotein
portion of the polypeptide that needs no further proteolytic processing for
activity. A second form of precursor is a pre-prohormone that consists of
the N-terminal signal sequence followed by a polyprotein, or prohormone,
sequence made up of two or more peptide domains linked together that
are subsequently liberated by cleavages during post-translational processing
of the prohormone.
The reason for synthesis of polypeptide hormones in
the form of precursors is only partly understood. The N-terminal signal
sequences function in the early stages of transport of polypeptide into the
secretory pathway. Prohormones, or polyproteins, often provide a source of
multiple bioactive peptides (see Fig. 3-4). However, many prohormones
contain peptide sequences that are removed by cleavage and have no known
biologic activity (cryptic peptides). Other peptides may serve as spacer
sequences between two bioactive peptides (e.g., the C peptide of proinsulin).
When a bioactive peptide is located at the carboxyl-terminus of the prohormone,
the N-terminal prohormone sequence may simply facilitate the
cotranslational translocation of polypeptide in the endoplasmic reticulum
(see Fig. 3-6).
Схема. Первичная структура некоторых прогормонов = Primary structures of some prohormones.
Модификация: Melmed S., Polonsky K.S., Larsen P.R., Kronenberg H.M., Eds. Williams Textbook of Endocrinology, 12th ed., Saunders, 2011, 1816 p., см.: Физиология человека: Литература. Иллюстрации.
Примечание.
The shaded areas of
prohormones denote regions of sequence that constitute known biologically
active peptides after post-translational cleavage from the prohormone.
Sequences indicated by hatching denote regions of precursor that alter the
biologic specificity of that region of precursor. For example, the precursor
contains the sequence of г-melanocyte-stimulating hormone (г-MSH), but
when the latter is covalently attached to the CLIP peptide, it constitutes
adrenocorticotropic hormone (ACTH). Somatostatin-28 (SS-28) is an
amino-terminally extended form of somatostatin-14 (SS-14) that has higher
potency than SS-14 on certain receptors. The neurophysin sequence linked
to the carboxyl-terminus of vasopressin (ADH) functions as a carrier protein
for the ADH hormone during its transport down the axon of neurons in
which it is synthesized. Figure 3-5 Subcellular organelles involved in transport and secretion of polypeptide hormones or other secreted proteins within a protein-secreting cell.
(1) Synthesis of proteins on polyribosomes attached to rough endoplasmic reticulum (RER) and vectorial discharge of proteins through the membrane into
the cisterna. (2) Formation of shuttling vesicles (transition elements) from endoplasmic reticulum followed by their transport to and incorporation by the
Golgi complex. (3) Formation of secretory granules in the Golgi complex. (4) Transport of secretory granules to the plasma membrane, fusion with the plasma
membrane, and exocytosis resulting in the release of granule contents into the extracellular space.
Notice that secretion may occur by transport of secretory vesicles and immature granules or by transport of mature granules. Some granules are taken up and hydrolyzed by lysosomes (crinophagy). Golgi, Golgi complex; SER, smooth endoplasmic reticulum. (From Habener JF. Hormone biosynthesis and secretion. с. 44.
Схема. Клетки, секретирующие белки. Субклеточные органеллы, вовлечённые в процессы секреции и транспорта полипептидных гормонов и других белков = Subcellular organelles involved in transport and secretion of polypeptide hormones or other secreted proteins within a protein-secreting cell. Модификация: Melmed S., Polonsky K.S., Larsen P.R., Kronenberg H.M., Eds. Williams Textbook of Endocrinology, 12th ed., Saunders, 2011, 1816 p., см.: Физиология человека: Литература. Иллюстрации.
Примечание:
с. 44 Figure 3-5 Subcellular organelles involved in transport and secretion of polypeptide hormones or other secreted proteins within a protein-secreting cell.
(1) Synthesis of proteins on polyribosomes attached to rough endoplasmic reticulum (RER) and vectorial discharge of proteins through the membrane into
the cisterna. (2) Formation of shuttling vesicles (transition elements) from endoplasmic reticulum followed by their transport to and incorporation by the
Golgi complex. (3) Formation of secretory granules in the Golgi complex. (4) Transport of secretory granules to the plasma membrane, fusion with the plasma
membrane, and exocytosis resulting in the release of granule contents into the extracellular space. Notice that secretion may occur by transport of secretory
vesicles and immature granules or by transport of mature granules. Some granules are taken up and hydrolyzed by lysosomes (crinophagy). Golgi, Golgi
complex; SER, smooth endoplasmic reticulum. (From Habener JF. Hormone biosynthesis and secretion. In: Felig P, Baxter JD, Broadus AE, et al, eds. Endocrinol
Metab. New York, NY: McGraw-Hill, 1981:29-59.)
Разрешается некоммерческое цитирование материалов данной энциклопедии при условии полного указания источника заимствования: имени автора, названия и WEB-адреcа данной энциклопедии
