1887

Abstract

SUMMARY

The biosynthesis of carbamoyl phosphate (CP), a metabolic precursor of arginine and the pyrimidines was investigated in the hyperthermophilic archaeon . The half-life of CP was found to be less than 2 s in the optimum temperature range of this organism (100-102 °C). The carbamoyl-phosphate synthase (CPSase) of uses ammonia as the nitrogen donor, and not glutamine like all micro-organisms investigated so far. The of the enzyme, which is devoid of regulatory properties, is 70000, at variance with that of known CPSases. The possible significance of these findings with regard to hyperthermophilic nitrogen metabolism is discussed. Competition experiments with crude extracts indicated a marked preference of ornithine carbamoyltransferase (OTCase) for CP synthesized by CPSase rather than for CP added to the reaction mixture. In addition, the bisubstrate analogue --phosphonoacetyl-L-ornithine inhibits the formation of citrulline from bicarbonate, ammonia, ATP and ornithine much less than its synthesis from ornithine and CP in the presence of free OTCase. Such results suggest that, , CPSase and OTCase associate in a complex able to channel CP. Such a channelling may confer protection to CP, thus avoiding the accumulation of toxic amounts of cyanate arising from its decomposition as well as the waste of the two molecules of ATP required for its synthesis.

Loading

Article metrics loading...

/content/journal/micro/10.1099/13500872-141-5-1093
1995-05-01
2019-10-15
Loading full text...

Full text loading...

http://instance.metastore.ingenta.com/content/journal/micro/10.1099/13500872-141-5-1093
Loading
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error