Proposed Enzymes of Auxin Biosynthesis and Their Regulation II. Tryptophan Dehydrogenase Activity in Plants. |
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Authors: | M Kutaček Sultana Terziivanova-dimova |
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Institution: | (1) Institute of Experimental Botany, Czechoslovak Academy of Sciences, 166 30 Praha 6, Ke dvoru 15, Czechoslovakia;(2) Institute of Plant Physiology “M. Popov”, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria |
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Abstract: | In pea, maize and tomato plants a hitherto undescribed L-tryptophan dehydrogenase activity (TDH) has been detected. This enzyme
catalyzes the reversible formation of indolepyruvic acid (IPyA) from L-tryptophan (L-trp). TDH and L-glutamate dehydrogenase
(GDH), related enzymes in their mode of action, could be separated by gel chromatography. Enzymatic activity of TDH was sustained
by both pyridine coenzymes NAD/NADP. With pea TDH the coenzyme NAD displays, at optimum pH 8.5 and at room temperature, only
about 40-70 % of the activity of NADP. The amination of IPyA is catalysed more actively than the deamination of L-trp. L-trp/IPyA,
L-glu/ketoglutarate, L-ala/pyruvate reacted as dehydrogenase substrates; L-phe/ phenylpyruvate, D-trp and D-phe did not react
with pea enzyme extracts. A considerable similarity between the active centres of TDH and GDH has been found using inhibitors:
absence of heavy metals, presence of a carbonyl group, indispensibility of bivalent ions for the enzyme activity. Pea TDH
and GDH were distinctly inhibited by sodium azide. For the activity of TDH the presence of SH groups is less important than
for GDH. The TDH activity in the investigated plants was lower than the GDH activity. The possible role of TDH in the regulation
of the IPyA pool is discussed.Doc. RNDr. PhMr. M. Kutáček died on 28 November, 1989. The final form for print was prepared by dr. Ivana Machdckovd of the
same Institute, who will also answer the reprint requests. Received June 6, 1990; accepted October 10, 1990 |
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