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  • C-peptide  (1)
  • Chemistry  (1)
  • Half-of-the-sites reactivity  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Induced versus pre-existing asymmetry models for the half-of-the-sites reactivity effect in bovine liver uridine diphosphoglucose dehydrogenase
    Amsterdam : Elsevier
    BBA - Enzymology 614 (1980), S. 242-255 
    Details
    ISSN: 0005-2744
    Keywords: (Bovine liver) ; Asymmetry model ; Half-of-the-sites reactivity ; Uridine diphosphoglucose dehydrogenase
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2744(80)90214-4
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  • 2
    Electronic Resource
    Electronic Resource
    Insulin inhibits its own secretion from isolated, perifused human pancreatic islets (1995)
    Springer
    Acta diabetologica 32 (1995), S. 75-77 
    Details
    ISSN: 1432-5233
    Keywords: Islets of Langerhans ; C-peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It is still a controversial question whether insulin suppresses its own secretion. We prepared pure human islets from three pancreases by collagenase digestion and density gradient purification. Aliquots of 200 islet equivalents (IE, 150-μm sized-islets) were sequentially perifused at 37°C with 3.3 mmol/l glucose (3.3G, 40 min), 16.7 mmol/l glucose (16.7G, 30 min) and again 3.3G (30 min) after 24 h, 37°C culture in CMRL 1066 medium with or without the addition of either 200 or 400 μU/ml human insulin in the incubation medium (6 replicates each). Insulin secretion was assessed by C-peptide (Cp) measurement in the perufusate. Without added insulin (C) and with 200 (Ins200) or 400 (Ins400) μU/ml added insulin, basal Cp release was 0.12±0.03, 0.14±0.02 and 0.14±0.04 ng/ml, respectively. At 16.7G, the first-phase secretion peak (expressed as Cp value) was significantly lower with Ins200 (0.47±0.13 ng/ml,P〈0.02) and Ins400 (0.68±0.15 ng/ml,P〈0.05) than C (0.83±0.15 ng/ml). The second-phase secretion peak was also significantly (P〈0.05) reduced with added insulin (Ins200: 0.47±0.08 ng/ml; Ins400: 0.45±0.07 ng/ml) than in its absence (C: 0.65±0.09 ng/ml). Accordingly, total Cp secretion was lower with Ins200 (10.6±2.3 ng/ml,P=0.03) and Ins400 (11.8±2.3 ng/ml) than with C (16.0±2.2 ng/ml). Thus, the addition for 24 h of either 200 or 400 μU/ml insulin in the culture medium caused a significant decrease of insulin (as assessed by Cp measurement) secretion from perifused human islets, suggesting that feedback suppression of insulin release is at least in part due to a direct action of insulin on the islets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00569560
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  • 3
    Electronic Resource
    Electronic Resource
    Raman and infrared spectroscopic study of the molecular characterization of the biocompatibility of prosthetic biomaterials (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 25 (1994), S. 109-114 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra were obtained directly in a non-destructive and non-invasive way from the biomaterials PMMA [poly(methyl methacrylate)], HDPE (high-density polyethylene), α-Al2O3 (alumina) and HA (hydroxyapatite) constituting the components (bone cement, acetabular cup, ball and stem coated with ceramic) of a hip prosthesis. The aim was to give an objective contribution at a molecular level to predict their biocompatibility. In particular, Raman spectra of explanted PMMA bone cements do not show the 1640 cm-1 band due to the stretching mode of C=C unsaturated centres. Moreover, conformational changes of PMMA following the implant appear in the spectra in the range 1100-500 cm-1, where conformational marker bands at 985, 968, 601 and 565 cm-1 are present. The limited number of HDPE explanted acetabular cups did not allow unequivocal Raman results to be obtained by means of band deconvolution in the region between 1500 and 1000 cm-1, regarding the changes in the crystalline, amorphous and interfacial contents of the acetabular cup surfaces following the implant. α-Al2O3 proved to be a ceramic with good biocompatibility as a biomaterial constituting a hip prosthesis. As regards the stem coating, Raman and Fourier transform IR spectra of HA pre-coating and HA coating on metal implants show spectroscopic modifications due to structural and chemical changes with formation of other calcium phosphates. The development of new bioactive coatings containing precursors of bone growth and able to promote osteogenesis is outlined.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250250116
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