Exogenous l-tyrosine metabolism and dhurrin turnover in sorghum seedlings

  • Bough W
  • Gander J
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It was shown that dhurrin (p-hydroxymandelonitrile-β-glucopyranoside) was actively metabolized by etiolated Sorghum vulgare seedlings. A turnover rate of about 0·05 μmole/hr was found in seedlings containing 1·0 μmole dhurrin/shoot. These studies showed a logarithmic decrease in the specific activity of14C labelled dhurrin when unlabelled l-tyrosine was administered to the seedlings. The increase in specific activity of dhurrin was shown to be a logarithmic function of time when seedlings were administered [2-14C]-l-tyrosine. In addition, it was concluded that a major fraction of the dhurrin in the seedlings was derived from endogenous sources rather than from exogenously supplied l-tyrosine. Sorghum seedlings were shown to metabolize [1-14C]-, [2-14C]-, [3-14C]-, and [U-14C]-l-tyrosine to14CO2. Based on the time course of14CO2released from l-tyrosine labelled in carbon atom 1, 2 or 3 as compared to uniformly labelled l-tyrosine, the data suggest that sorghum seedlings catabolized a portion of the aromatic ring carbon atoms to14CO2. The dhurrin present 50 hr after administering [2-14C]-l-tyrosine represented only 3% of the14C found in the various extracts, residues and CO2. A procedure for isolating dhurrin from perchloric acid extracts is described. © 1972.

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  • Wayne A. Bough

  • J. E. Gander

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