1887

Abstract

Summary: Some kinetic properties of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase from , a marine, facultatively heterotrophic, sulphur-oxidizing bacterium and putative symbiont of (Montagu), a bivalve mussel, have been determined. The kinetic parameters for the CO/Mg-activated enzyme were: (RuBP) 24·3 μM, (CO) 125·5 μM, (O) 900 μM and (Mg) 1·53 mM. The low CO affinity suggests that may possess a CO-concentrating mechanism. RuBP oxygenase activity was inhbited by increasing CO concentration. Divalent metal ions were essential for RuBP carboxylase activity; activity of the Mg-free enzyme could be restored by the addition of Mg, Mn or Ca. The pH optimum was 7·8. The temperature optimum for RuBP carboxylase activity was 55 °C, although the enzyme rapidly lost activity at this temperature. An Arrhenius plot was biphasic, with a break at 40 °C. The activation energies were 55·5 × 10 J mol and 32·9 × 10 J mol> over the temperature ranges 10-40 °C, and 1·47 between 40-55 °C, RuBP carboxylase activity was stable at 35 °C, the optimum growth temperature of and at 7·5 °C, the temperature of the habitat of , but the activity was 40% and 3·5%, respectively, of the potential activity at 55 °C. RuBP carboxylase activity was stimulated by NaCl concentrations of up to 0·3 m, with a maximum (33%), occurring between 0·1 and 0·2 m-NaCl. At higher concentrations of NaCl (>0·3 m) RuBP carboxylase activity was inhibited.

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/content/journal/micro/10.1099/00221287-137-7-1491
1991-07-01
2019-10-14
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http://instance.metastore.ingenta.com/content/journal/micro/10.1099/00221287-137-7-1491
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