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The transport and metabolism of urea in Chara australis: II. Urease and the distribution of transported urea

Journal Article


Abstract


  • The ureolytic enzyme in Chara was investigated. This enzyme was shown to be a urease with an unusually high affinity for urea(Km =θ158 mmol m-3). Little inhibition of urease activity was found when intact Chara cells were exposed to the urease inhibitors hydroxyurea, acetohydroxamic acid and N-ethylmaleimide, although there was some inhibition of urea uptake.The distribution of radioactivity amongst the amino acid, organic acid and sugar/neutral fractions, determined by ion-exchange chromatography, was very similar whether the Chara internodes were exposed to 14C-urea or to H14CO3. This suggests that the fraction of the urea-carbon liberated by the urease as CO2 and retained by the cell is used in photosynthetic carbon-fixation. During the initial 15 min of 14C-urea uptake, label appears in the vacuole only in the form of unmetabolized urea. After this time a variety of labelled compounds appear in the vacuole, presumably reflecting the gradual movement of carbon-fixation products from the chloroplasts to the cytoplasm and thence into the vacuole. © 1988 Oxford University Press.

Publication Date


  • 1988

Citation


  • Wilson, M. R., & Walker, N. A. (1988). The transport and metabolism of urea in Chara australis: II. Urease and the distribution of transported urea. Journal of Experimental Botany, 39(6), 753-761. doi:10.1093/jxb/39.6.753

Scopus Eid


  • 2-s2.0-0003184899

Start Page


  • 753

End Page


  • 761

Volume


  • 39

Issue


  • 6

Abstract


  • The ureolytic enzyme in Chara was investigated. This enzyme was shown to be a urease with an unusually high affinity for urea(Km =θ158 mmol m-3). Little inhibition of urease activity was found when intact Chara cells were exposed to the urease inhibitors hydroxyurea, acetohydroxamic acid and N-ethylmaleimide, although there was some inhibition of urea uptake.The distribution of radioactivity amongst the amino acid, organic acid and sugar/neutral fractions, determined by ion-exchange chromatography, was very similar whether the Chara internodes were exposed to 14C-urea or to H14CO3. This suggests that the fraction of the urea-carbon liberated by the urease as CO2 and retained by the cell is used in photosynthetic carbon-fixation. During the initial 15 min of 14C-urea uptake, label appears in the vacuole only in the form of unmetabolized urea. After this time a variety of labelled compounds appear in the vacuole, presumably reflecting the gradual movement of carbon-fixation products from the chloroplasts to the cytoplasm and thence into the vacuole. © 1988 Oxford University Press.

Publication Date


  • 1988

Citation


  • Wilson, M. R., & Walker, N. A. (1988). The transport and metabolism of urea in Chara australis: II. Urease and the distribution of transported urea. Journal of Experimental Botany, 39(6), 753-761. doi:10.1093/jxb/39.6.753

Scopus Eid


  • 2-s2.0-0003184899

Start Page


  • 753

End Page


  • 761

Volume


  • 39

Issue


  • 6