Partial Purification and Characterization of Ornithine Carbamoyl Transferase (OCT) from the Cyanobacterium Nostoc sp. Strain PCC 73102 |
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Authors: | Eva Jansson Peter Lindblad |
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Institution: | Department of Physiological Botany, Uppsala University, Villav?gen 6, S-752 36 Uppsala, Sweden, SE
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Abstract: | Ornithine carbamoyl transferase (OCT) catalyzes the formation of citrulline and orthophosphate from ornithine and carbamoyl
phosphate. We have partially purified OCT from the filamentous cyanobacterium Nostoc sp. strain PCC 73102, using ammonium sulfate precipitation (35–55%), a gel-filtration column (Sephacryl S-200), followed
by an affinity column (Sepharose-6B-PALO). The partially purified OCT was analyzed on native-PAGE and shown to be an active
enzyme with an estimated molecular weight of approximately 80 kDa. The isoelectric point was determined to be about 6.2. Varying
the ornithine concentration resulted in a hyperbolic response of the reaction velocity at lower concentrations. Ornithine
concentrations above 2 mM inhibited the enzyme. A hyperbolic response of the OCT reaction was observed when increasing the
carbamoyl phosphate concentration. From a double reciprocal plot, a saturation concentration of 0.8 mM and a Vmax of 0.4 U/mg may be calculated. None of the tested compounds (argininosuccinate, arginine, aspartic acid, urea) had any significant
positive effect on the in vitro activity of the partially purified OCT. Moreover, at concentrations higher than 10 mM, all
tested compounds had an inhibitory effect.
Received: 23 March 1998 / Accepted: 6 May 1998 |
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