Studies on carbamoyl phosphate-<scp>l</scp>-ornithine Carbamoyltransferase from ox liver

Joseph, R. L.; Baldwin, Ernest; Watts, D C

doi:10.1042/bj0870409

Cited by 25 publications

(9 citation statements)

References 9 publications

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“…Figure 1 shows the Lineweaver-Burk plot for ornithine at several fixed concentrations of carbamoylphosphate. The family of lines agrees with the pattern observed for highly purified ox-liver enzyme (7) and suggests a similar ternary complex reaction mechanism. The intercept on the x-axis corresponds to a Ks of 5.0 mm for ornithine.…”

Section: Resultssupporting

confidence: 75%

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Mode of Action of the Toxin from Pseudomonas phaseolicola

Tam

Patil

1972

Plant Physiol.

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Section: Resultssupporting

confidence: 75%

“…Assays were routinely limited to 10 min due to lability of carbamoylphosphate. Beyond 20 min the reaction rate decreases, probably due to the build-up of P,, a known inhibitor of OCT (7). Although the temperature optimum is 40 C under these conditions, all assays were performed at 37 C to limit decomposition of carbamoylphosphate.…”

Section: Resultsmentioning

confidence: 99%

Mode of Action of the Toxin from Pseudomonas phaseolicola

Tam

Patil

1972

Plant Physiol.

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“…The apparent Michaelis constants for ornithine and carbamoylphosphate found with crude cell-free extracts of H . salinarium are of the same order of magnitude as those determined for non-halophilic ornithine carbamoyltransferases [17,18,22,23].…”

Section: 'supporting

confidence: 60%

“…Inhibitory effects by the buffers used account for some of the discrepancies. Enzyme from bovine liver has a pH optimum between 8 and 8.5 [17,18]. Enzymes from Bacillus licheniformis have a pH optimum of 8.5 [19].…”

Section: Discussionmentioning

confidence: 99%

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Ornithine Carbamoyltransferase from Halobacterium salinarium

Dundas¹

1972

Eur J Biochem

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The enzymatic properties of purified ornithine carbamoyltransferase from Halobacterium salinarium have been studied and compared with those of the enzyme from non-halophilic organisms, and with those of other enzymes from halophilic organisms.The enzyme is stable and active in high concentrations of NaCl, KC1, RbCl and CsCl as are other enzymes from halophilic organisms. No activity could be measured a t any concentrations of LiCl. The pH optimum for activity is similar for ornithine carbamoyltransferase from halophilic and nonhalophilic organisms. The enzyme is effectively protected against denaturation by the presence of any of its substrates, ornithine, citrulline or carbamoylphosphate, a phenomenon found for many enzymes from non-halophilic organisms. Ornithine carbamoyltransferase from H . salinarium shows a cooperative effect in binding ornithine, similar allosteric effects are found for the enzyme from non-halophilic organisms. Phosphate inhibits enzyme activity competitively versus carbamoylphosphate for enzymes from both halophilic and non-halophilic organisms.Ornithine carbamoyltransferase from H . salinarium accordingly seems to be subject to control mechanisms similar to those operative for the non-halophilic enzyme. There is no evidence that unusual or specific controls are operative for the enzyme in high salt concentrations. The unique properties of the halophilic enzyme are related only to its ability to function a t high salt concentrations.Halobacteria grow only in media containing 12 to 20°/, NaCl and many strains are able to proliferate in media with near saturation concentrations of NaC1. Enzymes from Halobacteria have adapted to the very high intercellular concentrations of salts in the organisms and are rapidly inactivated in the absence of salt. Many of these enzymes show optimal activities in the presence of NaCl concentrations higher than 3 M [l].

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