Ornithine transcarbamylase fromLactobacillus buchneri NCDO110 |
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Authors: | María C Manca de Nadra Aída A Pesce de Ruiz Holgado Guillermo Oliver |
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Institution: | (1) Instituto de Microbiología, Faculty of Biochemistry, Chemistry, and Pharmacy, Univrsidad Nacional de Tucumán, Chacabuco, 145-4000 Tucumán, Argentina;(2) Centro de Referencia para Lactobacilos (CERELA), Tucumán, Argentina |
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Abstract: | Ornithine transcarbamylase (OTCase) (E.C.2.1.3.3) was partially purified fromLactobacillus buchneri NCDO110. It was stabilized by the presence of glycerol. The optimal pH for enzyme activity is 8.5. The positive cooperativeness was observed among ornithine molecules at pH values different from the optimum. The Mr of the enzyme was calculated to be 162,000 by gel filtration on Ultrogel ACA-34. Maximum activity occurred at 35°C. G* of the reaction was calculated from Arrhenius plot. The values were 9100 cal mol–1 below 35°C, and 4300 cal mol–1 above 35°C. The Km value for carbamylphosphate was 7.1×10–4
M, and the Km for ornithine was 1.6×10–3
M, under the conditions described here. Dead-end inhibition analysis was performed with norvaline, which is a structural analogue of ornithine. Norvaline acted as a noncompetitive inhibitor when carbamylphosphate was the variable substrate, and as a competitive inhibitor when ornithine was the variable substrate. The results are consistent with a ping-pong mechanism. |
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