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Identification of proline-specific carboxypeptidase localized to brush border membrane of rat small intestine and its possible role in protein digestion (1989)

Erickson, Roger H. ; Song, S. ; Yoshioka, Masahiro ; [et al.]

Springer

Digestive diseases and sciences 34 (1989), S. 400-406

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ISSN: 1573-2568

Keywords: small intestine ; brush border membrane ; carboxypeptidase P

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Abstract A proline-specific carboxypeptidase (carboxypeptidase P, EC 3.4.12.-) was identified and partially characterized in the brush border membrane fraction of rat intestinal enterocytes and shown to be distinct from pancreatic proteases. The carboxypeptidase activity of isolated brush border membranes, with Z-Gly-Pro-Leu as substrate, was 43 nmol/min/mg protein representing a 16-fold purification when compared with mucosal cell homogenates. Activity was maximal in the middle region of the small intestine, and villus cells had twice the activity of crypt cells. Carboxypeptidase activity was maximal at pH 7.0, was stimulated by divalent cations, and was inhibited by metal chelating agents, suggesting that it is a metalloenzyme. The enzyme had the highest activity with synthetic peptides containing proline penultimate to the carboxy terminus. In vivopatterns of hydrolysis and absorption of amino acids from Z-Pro-Trp were examined using an intestinal perfusion technique. These studies indicate that brush border membrane carboxypeptidase may play an important role in the digestion of prolinecontaining peptides and proteins.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01536262

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Effect of intramolecular and intermolecular exchange processes on the 1H NMR spectra of 2-chloro-1,3,2-dioxarsolanes (1987)

Song, S. K. ; Watkins, C. L. ; Krannich, L. K.

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 25 (1987), S. 484-488

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ISSN: 0749-1581

Keywords: 1H NMR ; 13C NMR ; 2-Chloro-1,3,2-dioxarsolanes ; Intra- and inter-molecular exchange ; Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The 1H and 13C NMR spectra of solutions of 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxarsolane (1) and 2-chloro-1,3,2-dioxarsolane (2) are reported as a function of temperature, concentration and solvent. These data indicate rapid intramolecular conformational averaging for (1) and (2) under all the conditions investigated. Additionally, intermolecular conformational averaging processes are shown to be present. The kinetic parameters for intermolecular exchange were obtained from line shape analysis of the 1H NMR data. These results indicate the intermolecular exchange to be bimolecular in nature, involving a four-centered transition state. The O—CH2—CH2-O torsional angle of (2) has been calculated from the analysis of its AA′BB′ 1H NMR spectral patterns, obtained at low concentrations in the absence of intermolecular exchange.

Additional Material: 2 Ill.