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Proinsulin to insulin

In PCI/3-deficient mice, reduction of GnRH by about 80% was observed as well as decreases in GLP-1 and GLP-2 (46). Reduction in processing of proinsulin to insulin was observed in PCI/3-deficient mice (47). Interestingly, no change in vasopressin occurred, and little change in POMC-derived peptide hormones were observed in the PCl/3-deficient mice compared with wild-type controls (48). [Pg.1231]

Severe block in processing of proinsulin to insulin accompanied by elevation of des-64,65 proinsulin intermediates in islets of mice lacking prohormone convertase 1/3. Proc. Natl Acad. Sci. U.S.A. 66. 2002 99 10299-10304. [Pg.1235]

High proinsulin concentrations are usually noted in patients with benign or malignant j3 ceil tumors of the pancreas. Most patients with fl-cell tumors have increased insuhn, C-peptide, and proinsulin concentrations, but occasionally only proinsulin is increased because the tumors have defective conversion of proinsulin to insulin. Despite its low biological activity, proinsuHn production may be adequate to produce hypoglycemia. In addition, a rare form of familial hyperproinsulinemia, produced by impaired conversion to insulin, has been described. Measurement of proinsulin can... [Pg.850]

Conversion of proinsulin to insulin and C-peptide in secretory granules involves site-specific cleavages at the Arg-Arg and Lys-Arg sequences (Figure 22-6) these serve as signals for proteolytic processing of many other proteins. Cleavage occurs at the C-terminal end of each pair by trypsin-like enzymes and is followed by... [Pg.491]

Zn + is released when insulin is secreted. Conversion of proinsulin to insulin in the secretory granule is not complete and some proinsulin is also released upon secretion of insulin. Proinsulin has less than 5% of the biological activity of insulin. The C-peptide has no physiological function but assay of C-peptide helps distinguish between endogenous and exogenous sourees of insulin. [Pg.491]

C-peptide is cosecreted with insulin by the pancreatic P-cells as a by-product of the enzymatic cleavage of proinsulin to insulin. C-peptide and insulin are secreted into the portal circulation in equimolar concentrations. ... [Pg.467]

Protnsuttn. Single chain insulin precursor consisting of the insulin A and B chains and a connecting polypeptide (C-peptide). which contains 30-35 amino acids the number and sequence of these amino adds are species da -pendent. Its presence was discovered in a human islet cell adenoma D. F. Steiner, P. E. Oyer. Proc. Nat, Acad. Set USA 57, 473 (1967). Conversion of proinsulin to insulin has a half-time of about 1 hour in rat islets in vitro it is postulated that proteolytic enzymes cleave proinsulin at the sites... [Pg.1235]

FIGURE 60-1 Human proinsuUn and its conversion to insulin. The amino acid sequence of human proinsulin is shown. By proteolytic cleavage, four basic amino acids (residues 31, 32, 64, and 65) and the connecting peptide are removed, converting proinsulin to insulin. The sites of action of the endopeptidases PC2 and PC3 are shown. [Pg.1038]

After proteins emerge from the ribosome, they may undergo posttranslafional modifications. The initial methionine is removed by specific proteases methionine is not the N-terminal amino acid of all proteins. Subsequently, other specific cleavages also may occur that convert proteins to more active forms (e.g., the conversion of proinsulin to insulin). In addition, amino acid residues within the peptide chain can be enzymatically modified to alter the activity or stability of the proteins, direct it to a subcellular compartment, or prepare it for secretion from the cell. [Pg.268]

Fig 26.10. Cleavage of proinsulin to insulin. Proinsulin is converted to insulin by proteolytic cleavage, which removes the C-peptide and a few additional amino acid residues. Cleavage occurs at the arrows. From Murray RK, et al. Harper s Biochemistry, 23rd Ed. Stanford, CT Appleton Lange, 1993 560. [Pg.484]

Newly synthesized polypeptides are frequently processed before they reach the form in which they have biological activity. We have already mentioned that, in prokaryotes, W-formylmethionine is cleaved off. Specihc bonds in precursors can be hydrolyzed, as in the cleavage of preproinsulin to proinsulin and of proinsulin to insulin (Figure 12.22). Proteins destined for export to specihc parts of the cell or from the cell have leader sequences at their N-terminal ends. These leader sequences, which direct the proteins to their proper destination, are recognized and removed by specihc proteases associated with the endoplasmic reticulum. The hnished protein then enters the Golgi apparatus, which directs it to its hnal destination. [Pg.354]

There are several reports suggesting that cathepsin B is involved in generation of native peptides from their precursors. Cathepsin B converts proinsulin to insulin (111) and proalbumin to albumin (112) in vitro. However, it is likely that a proteinase(s) such as ER or secretory-vesicle bound cathepsin B in combination with carbox3q)ep-tidase may function in the processing of peptide hormones or secretory proteins. [Pg.94]

The enzymes causing the conversion of proinsulin to insulin are found in secretory granules. Two enzymes are involved an endopeptidase with trypsin-... [Pg.508]

The conversion of proinsulin to insulin raises a number of intriguing questions. First, is this phenomenon unique Second, why does the structural gene code for an inactive protein The phenomenon is certainly not unique although all details of structure and conversion of the prohormone into hormone are not known. Prohormones of vasopressin, parathormone, gastrin, glucagon, MSH and ACTH have been known to exist. In the case of insulinoma and parathormone adenoma the tumors may secrete large amounts of the extended hormones that appear in the blood and may serve as a diagnostic tool [196]. [Pg.509]

Insulin in the body is derived from its precursor molecule proinsulin. During the conversion of proinsulin to insulin, a small peptide (C-peptide) is released by enzymic action. Measurement of this peptide in serum provides a measure of pancreatic -cell function, even in patients on insulin. C-pep-tide determination can be used in the evaluation of a number of metabolic conditions, e.g. brittle diabetes, insulinoma. [Pg.101]

Secretion. The process of insulin secretion involves the movement of the secretory granules, in which the conversion of proinsulin to insulin occurs , to the periphery of the cell through a mlcrotubular-microfllament-ous system. The participation of such a system has been experimentally confirmed by studying the influence of a series of drugs, known to interfere with the function and structure of microtubules and microfilaments, upon the 6-cellsAn abnormality of the microtubular system has also been suggested as a cause of the diabetic syndrome found in the spiny mouse . [Pg.183]


See other pages where Proinsulin to insulin is mentioned: [Pg.212]    [Pg.216]    [Pg.55]    [Pg.207]    [Pg.999]    [Pg.207]    [Pg.857]    [Pg.271]    [Pg.60]    [Pg.724]    [Pg.98]    [Pg.1235]    [Pg.1037]    [Pg.5872]    [Pg.162]    [Pg.163]    [Pg.534]    [Pg.182]    [Pg.24]   
See also in sourсe #XX -- [ Pg.163 ]




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