Peptide and insulin

C on both carbonyl oxygen atoms (Olah et al., 1971b). N-alkoxycarbonyl-substituted amino-acids are also carbonyl proto-nated in that medium (Olah and Brydon, 1970). Some simple peptides and insulin have also been studied (Olah et al., 1970a). 

The laboratory diagnosis of diabetes is made exclusively by the demonstration of hyperglycemia. Other assays, such as the OGTT, contribute to the classification and characterization. Although other tests (e.g., C-peptide and insulin analysis) have been proposed to assist in the diagnosis and classification of the disease, these do not at present have a role outside of research studies. ... 

Ward WK, Paquette TL, Frank BH, Porte D, Jr. A sensitive radioimmunoassay for human proinsuhn, with sequential use of antisera to C-peptide and insulin. Clin Chem 1986 32 728-33. 

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. ... 

Following to this strategy, Hatakeyama, Kikuchi, Yamato, and Okano (2006) prepared carboxyl-functionalised thermo-responsive coatings on tissue culture polystyrene by electron beam-induced copolymerisation of A-isopropylacrylamide and 2-carboxy-isopropylacrylamide. The subsequent co-immobilization of RODS, a cell adhesive peptide, and insulin was found to promote initial cell adhesion and growth while the cultured tissue monolayers still detach spontaneously upon temperature decrease. 

Gorczyca M., Augart C., and Budnik V. 1993. Insulin-like peptide and insulin-like receptor are localized at neuromuscular junctions in Drosophila. J. Neurosci. 13 3692-3704. 

Insulin is a 50 amino acid protein which, unlike many peptides, is not glycosylated. It is produced naturally as three chains, the A, B and C chains. The C chain links the A and B chains and is removed by the body when the insulin is activated, leaving the A and B chains linked by two S-S bridges (Fig. 27.3). The metal ion zinc is also involved in stabilising the peptide, and insulin is stored in pancreatic P-cells as a hexamer complexed with two zinc atoms. 

Proteins consist of large numbers of amino-acids joined by the p>eptide link —CO —NH — into chains, as shown in the diagram, where R and R" are amino-acid residues. These chains are called peptides and may be broken into smaller chains by partial hydrolysis (see peptides). Proteins may contain more than one peptide chain thus insulin consists of... 

Insulin and Amylin. Insulin is a member of a family of related peptides, the insulin-like growth factors (IGFs), including IGF-I and IGF-II (60) and amylin (75), a 37-amino acid peptide that mimics the secretory pattern of insulin. Amylin is deficient ia type 1 diabetes meUitus but is elevated ia hyperinsulinemic states such as insulin resistance, mild glucose iatolerance, and hypertension (33). Insulin is synthesized ia pancreatic P cells from proinsulin, giving rise to the two peptide chains, 4. and B, of the insulin molecule. IGF-I and IGF-II have stmctures that are homologous to that of proinsulin (see INSULIN AND OTHER ANTIDIABETIC DRUGS). 

Antidiabetic Drugs other than Insulin. Table 3 Actions of the incretin hormones GIP (glucose-dependent insulinotropic polypeptide, gastric inhibitory peptide) and GLP-1 (glucagon-like peptide-1)... 

The predominant cell type in the pancreatic islets of Langerhans. The main secretory product of the (3 -cell is the peptide hormone insulin which has vital actions for the control of nutrient homeostasis and cellular differentiation. 

Fig. 24.7 The conversion of preproinsulin to insulin by sequential removal of the signal peptide and the C fragment.

Proinsulin is proteolytically processed in the coated secretory granules, yielding mature insulin and a 34-amino acid connecting peptide (C peptide, Figure 11.1). The C peptide is further proteolytically modified by removal of a dipeptide from each of its ends. The secretory granules thus contain low levels of proinsulin, C peptide and proteases, in addition to insulin itself. The insulin is stored in the form of a characteristic zinc-insulin hexamer, consisting of six molecules of insulin stabilized by two zinc atoms. 

Hormones and neuronal activity affect brain glycogen metabolism. Glycogen is affected by hormones endogenous to the brain including vasoactive intestinal peptide and noradrenaline, as well as circulating hormones, such as insulin [61, 63, 64]. The mechanism whereby insulin exerts an effect on glycogen metabolism in brain has not been determined [63]. Glycogen metabolism in brain, unlike in other tissues, is controlled locally, due to differential local metabolic rates. 

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