Aminoacid metabolism in plants : the biosynthesis of [beta]-cyanoalanine and asparagine in lupins : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Biochemistry at Massey University

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Massey University
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β-Cyanoalanine synthase in etiolated seedlings of Lupinus angustifolius is found mainly in the mitochondrial fraction of the cotyledons and stems. In seedlings developing at 25°C in the dark it reaches a maximal concentration after 5 days, at the same time as asparagine accumulation is most rapid and other physiological changes occur. However, maximal ability to assimilate HCN gas to asparagine develops after 3 to 4 days, before asparagine accumulation begins. A partial purification of lupin β-cyanoalanine synthase is described and its distinction from cysteine synthase confirmed. Carbon-14 labelled substrates were supplied to etiolated seedlings of lupin in order to identify precursors of asparagine. Four carbon acids related to the TCA cycle were readily converted to asparagine i n vivo but not in vitro; the carbon skeleton of aspartate is retained in asparagine. Comparison of the distribution of label in the carbon skeletons of aspartate and asparagine from plants supplied carboxyl labelled fumarate shows a separation of the aspartate pool for asparagine biosynthesis from most cell aspartate. Metobolites that could be expected to give rise to cyanide and β-cyanoalanine are relatively ineffective as asparagine precursors. Thus the β-cyanoalanine pathway is not of major importance in asparagine biosynthesis in lupins.
Amino acids, Metabolism, Plants, Lupins, Lupines, Physiology