{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,24]],"date-time":"2025-10-24T12:57:15Z","timestamp":1761310635911,"version":"build-2065373602"},"reference-count":20,"publisher":"Wiley","issue":"3","license":[{"start":{"date-parts":[[2007,4,24]],"date-time":"2007-04-24T00:00:00Z","timestamp":1177372800000},"content-version":"vor","delay-in-days":7418,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"content-domain":{"domain":["scijournals.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["J of Chemical Tech &amp;amp; Biotech"],"published-print":{"date-parts":[[1987,1]]},"abstract":"<jats:title>Abstract<\/jats:title><jats:p>For the purpose of immobilizing urease (urea amidohydrolase, EC 3.5.1.5) for routine determination of urea, a covalent bond immobilization method on titanium (IV) chloride activated silica supports<jats:sup>1,2<\/jats:sup> was used. Several parameters were studied in order to optimize the residual activity upon immobilization and during operation. The kinetic constants of the immobilized enzyme form (K<jats:sub>m<\/jats:sub>=92 mmol dm<jats:sup>\u22123<\/jats:sup>, V<jats:sub>max<\/jats:sub>=752 \u03bcmole min<jats:sup>\u22121<\/jats:sup> mg<jats:sup>\u22121<\/jats:sup>) are much higher than those of the free preparation (K<jats:sub>m<\/jats:sub>=31 mmol dm<jats:sup>\u22123<\/jats:sup>, V<jats:sub>max<\/jats:sub>=128 \u03bcmole min<jats:sup>\u22121<\/jats:sup> mg<jats:sup>\u22121<\/jats:sup>). The optimum pH of the immobilized enzyme preparation was shifted to higher values, from pH 7\u00b74 to 8. The optimum temperatures for the immobilized and free forms were 75 and 65\u00b0C, respectively. The activation energy of the immobilized form is four times smaller than that of the free, indicating less sensitivity to temperature. It was also observed that the immobilized enzyme exhibits a higher heat stability than the free enzyme. From these studies the conditions for optimal operation and retention of stability of the immobilized enzyme were determined. The enzyme immobilized on the alkylamine derivative of porous silica can be reused at 37\u00b0C for several hours a day with 100% retention of its initial activity for at least 1200 h of total life (i. e. operating time at 37\u00b0C plus stationary time at 4\u00b0C).<\/jats:p>","DOI":"10.1002\/jctb.280390306","type":"journal-article","created":{"date-parts":[[2010,7,5]],"date-time":"2010-07-05T09:41:44Z","timestamp":1278322904000},"page":"201-213","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Urease immobilization on an alkylamine derivative of titanium (IV)\u2010porous silica: Kinetics and operational stability"],"prefix":"10.1002","volume":"39","author":[{"given":"Maria Barbara F.","family":"Martins","sequence":"first","affiliation":[]},{"given":"Maria Eugenia M.","family":"Cruz","sequence":"additional","affiliation":[]},{"given":"Juaquim M. S.","family":"Cabral","sequence":"additional","affiliation":[]},{"given":"John F.","family":"Kennedy","sequence":"additional","affiliation":[]}],"member":"311","published-online":{"date-parts":[[2007,4,24]]},"reference":[{"key":"e_1_2_1_2_2","doi-asserted-by":"publisher","DOI":"10.1002\/bit.260230912"},{"key":"e_1_2_1_3_2","unstructured":"Kennedy J. F.;Cabral J. M. S.Methods in Enzymology In press."},{"key":"e_1_2_1_4_2","first-page":"209","volume":"21","author":"Szabo A.","year":"1983","journal-title":"J. Clin. Chem. Clin. Biochem."},{"key":"e_1_2_1_5_2","doi-asserted-by":"crossref","unstructured":"Sundaram P. V.Cost analysis and viability of immobilized enzymes in routine analysis. In: Enzyme Engineering. Vol. 6 (Chibata Fukui Wingard Eds) Plenum Press New York 1982 pp.405\u2013407.","DOI":"10.1007\/978-1-4615-9290-7_93"},{"key":"e_1_2_1_6_2","doi-asserted-by":"crossref","unstructured":"Murachi T.Use of immobilized enzyme reactors in automated clinical analysis. In: Enzyme Engineering. Vol. 6 (Chibata Fukui Wingard Eds) Plenum Press New York 1982 pp.369.","DOI":"10.1007\/978-1-4615-9290-7_89"},{"key":"e_1_2_1_7_2","first-page":"251","article-title":"Highly sensitive flow injection analysis of glucose and uric acid in serum using an immobilized enzyme column and chemiluminescence","volume":"6","author":"Tabata M.","year":"1984","journal-title":"J. Appl. Biochem."},{"key":"e_1_2_1_8_2","doi-asserted-by":"publisher","DOI":"10.1016\/0003-2670(86)80004-6"},{"key":"e_1_2_1_9_2","doi-asserted-by":"publisher","DOI":"10.1016\/0300-9467(83)80079-3"},{"key":"e_1_2_1_10_2","doi-asserted-by":"publisher","DOI":"10.1016\/0141-0229(83)90060-1"},{"key":"e_1_2_1_11_2","unstructured":"Cardoso J. P.Ph.D. Thesis University of Birmingham UK (1977)."},{"key":"e_1_2_1_12_2","doi-asserted-by":"publisher","DOI":"10.1093\/clinchem\/8.2.130"},{"key":"e_1_2_1_13_2","doi-asserted-by":"publisher","DOI":"10.1016\/S0021-9258(19)52451-6"},{"key":"e_1_2_1_14_2","unstructured":"Cabral J. M. S.Ph.D. Thesis University of Lisbon Portugal."},{"key":"e_1_2_1_15_2","doi-asserted-by":"crossref","unstructured":"Goldstein L.Kinetic behaviour of immobilized enzyme systems. In: Methods in Enzymology. Vol. XLIV (Mosbach K. Ed.) Academic Press 1976 pp.397\u2013443.","DOI":"10.1016\/S0076-6879(76)44031-4"},{"key":"e_1_2_1_16_2","doi-asserted-by":"crossref","first-page":"234","DOI":"10.1093\/clinchem\/24.2.234","article-title":"Immobilized\u2010enzyme nylon tube reactors for routine determination of urea and citrulline in serum","volume":"24","author":"Sundaram P. V.","year":"1978","journal-title":"Clin. 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